States of Matter 66B

Quantities for each group

STUDENT EDITION

Inquiry Activity, p. 67 syringe (sealed at narrow end),water

Quick Lab, p. 79 pan, metric ruler, emptybeverage can, masking tape,hot plate, clock, tongs

Quick Lab, p. 90 250-mL Erlenmeyer flask,graduated cylinder,thermometer, dry ice

Exploration Lab, pp. 92–93500-mL beaker, crushed ice,thermometer, hot plate, clockwith second hand, test tube oflauric acid with thermometer,glass stirring rod, graph paper

TEACHER’S EDITION

Teacher Demo, p. 69 3 glass jars or bottles with lids, each having a noticeablydifferent diameter but aboutthe same volume; graduatedcylinder; water

Teacher Demo, p. 72 spray can of air freshener, 3 stopwatches

Build Science Skills, p. 75clay, CD case, textbook

Teacher Demo, p. 76 inflated balloons, refrigerator,warm place

Build Science Skills, p. 82plastic bag (dry cleaner or thin garbage bag), string, hair dryers

Teacher Demo, p. 86tray of ice cubes

Materials for Activities and Labs

Chapter Assessment

CHAPTER ASSESSMENT

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66C Chapter 3

Chemistry Refresher

States of Matter and Kinetic Theory 3.1

Solid, liquid, and gas are the common states of matter on Earth.However, almost all the matter in the observable universe existsas plasma. Plasma is formed when a gas is heated to temperaturesnear 10,000°C. At these temperatures, electrons can be lost dur-ing collisions between atoms or stripped by ionizing radiation.Because it contains mobile electrons, plasma can conduct anelectric current. On Earth, plasma occurs mainly in lightning dis-charges and fluorescent lights. Not every substance can exist inevery state. For example, some compounds that are solids atroom temperature—e.g., mercury(II) oxide or sodium iodate—will decompose before they melt or boil.

Solids such as rubber, asphalt, and glasses are classified as amor-phous solids because they lack the orderly internal structurefound in crystalline solids. With the data supplied by improvedinstruments, scientists now know that glasses contain regionswhere the arrangement of particles is orderly.

The kinetic theory appliesthe laws of mechanics to indi-vidual atoms or molecules. Itexplains the physical proper-ties of matter in terms of themotion of the particles. Twomajor contributors to the the-ory were James Joule (CountRumford) and James ClerkMaxwell. The theory worksbest for gases (because theeffect of attractive forces isminimal), but it can be appliedto liquids and solids.

The Gas Laws 3.2

Four variables are used to describe the behavior of a gas: tem-perature (T), pressure (P), volume (V), and amount. The amountof a gas is usually expressed as the number of moles (n). In 1662,Robert Boyle investigated the relationship between the volumeand pressure of a gas. Using a J-shaped tube, Boyle measured gaspressure (indicated by the height of mercury) and gas volume ata constant temperature. His conclusions are now known asBoyle’s law: P1V1 � P2V2.

Before you teach

Students may think thatparticles in gases havemore kinetic energy thanparticles in liquids or solids.They are confusing howfreely particles move withtheir speed of motion. Fora strategy to overcomethis misconception seeAddress Misconceptionson page 73.

Big IdeasOn Earth, matter is readily observed in three states: gas,liquid, and solid. The kinetic theory is used to explainthe behavior of these states of matter, including whatoccurs within a sample of a substance as the substancechanges from one state to another. The forces ofattraction that hold solids and liquids together are also a key factor.

Matter and Change In Section 3.3, students buildon knowledge from Chapter 2. They should realize thatphase changes are physical changes because compositiondoes not change during a phase change. You may need tostress that the molecules in ice, liquid water, and watervapor are identical. Only their arrangement is different.Because water is used as an example throughout thesection, be sure that students do not assume that allsubstances have exactly the same properties as water.For example, substances that are normally gases at roomtemperature must have boiling points below 20°C.

Forces and Motion To understand the generalproperties of solids, liquids, and gases, students mustenvision the constant motion of atoms and molecules.To further understand gases, students need to know that gas pressure in an enclosed container is caused byparticles colliding with the walls of their container.Section 3.2 focuses on the variables that affect thepressure of gases: temperature, volume, and number of particles. The section is organized so that you haveoptions for presenting the relationships between thevariables—qualitative descriptions of the factors thataffect gas pressure, graphs of Charles’s and Boyle’s laws,and mathematical expressions.

Energy Energy is transferred between a system and itssurroundings during a phase change. Students learn thatthe energy absorbed by material can overcome forces ofattraction between particles in the material or increasethe average kinetic energy of the particles.

From the AuthorDavid FrankFerris State University

In 1787, Jacques Charles made a graph of volume versus tem-perature in degrees Celsius for a gas at constant pressure. Thegraph showed that volume increased as temperature increased,but it did not represent a direct relationship because the straightline did not pass through the (0, 0) point. When the line on thegraph was extended beyond the data, the line crossed the x-axisat �273.15°C. This value is 0 K on the temperature scale devel-oped by Lord Kelvin (William Thompson). As shown on thegraph below, when Charles’s data is plotted using kelvins insteadof degrees Celsius, there is a direct relationship between the vari-ables and Charles’s law can be stated as V1/T1 = V2/T2.

Boyle’s law relates pressure andvolume. Charles’s law relatestemperature and volume. In1808, Joseph Gay-Lussac pro-posed the law that relatestemperature and pressure:There is a direct relationshipbetween the pressure of a gasand its kelvin temperature. Thecombined gas law describes allthree laws, but it doesn’taccount for moles of a gas.Because gas pressure is due to

the collision of particles, the number of particles in a sample ofgas is key, not the type of particles. Amedeo Avogadro first statedthis important idea as a hypothesis in 1811: Equal volumes ofgases at the same temperature and pressure contain the samenumber of particles. The equation that relates all four variables—V, T, P, and n—is the ideal gas equation PV � nRT, where the idealgas constant R equals 8.314 kPa•L/mol•K.

Phase Changes 3.3

A phase change involves the transfer of energy between a system andits surroundings. As a substance changes from a solid to a liquid toa gas, the degree of order in the system increases. When a phasechange is from a more-ordered to a less-ordered state, energy mustbe absorbed by the system to overcome attractive forces. When thechange is to a more-ordered state, energy is released by the systemto the surroundings.

Build Reading Literacy

Predict

Previewing to Predict ContentStrategy Help students activate their prior knowledge about a topic and become actively engaged in reading. The process ofmaking and confirming predictions also helps students correcttheir own misconceptions. Before students begin, have them focuson one topic in Chapter 3, such as the introductory paragraph onp. 68 and Describing the States of Matter on pp. 68–70.

Example1. Introduce students to the topic by having them read theheading and subheadings.2. Ask students what they think they will learn about the topic.3. Have a student read aloud the first Key Concept underReading Focus at the top of the page.4. Have another student read aloud the Comparing andContrasting instructions in the Reading Strategy.5. Based on what they’ve read so far, ask students to predict thecontent of the section. Write their predictions on the board.6. Have a student read aloud the boldfaced key statement on p. 68. Then, have other students read aloud the boldfaced termson p. 69.7. Discuss with students the predictions on the board. Allowthem to revise the predictions if they wish.8. Have students read through the section independently.Afterwards, ask which of their predictions were confirmed.Point out that there’s nothing wrong with making an incorrectprediction. Predicting can help readers learn more about a topic.

See p. 77 for a script on how to use the predicting strategywith students. For additional Build Reading Literacystrategies, see pp. 69 and 85.

Some students think thatgases, such as those in air,do not have mass. But theparticles in air must havemass to exert pressure. For a strategy to overcomethis misconception seeAddress Misconceptionson page 79.

States of Matter 66D

For: Teaching methods for states of matterVisit: www.SciLinks.org/PDLinksWeb Code: ccn-0399

Temperature (K)

0˚C

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lum

e (m

L)

Charles's Law

00 50 100 150 200 250 300

2

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94 Chapter 3

CHAPTER

3 Study Guide3.1 Solids, Liquids, and Gases

Key Concepts

• Materials can be classified as solids, liquids, orgases based on whether their shapes and volumesare definite or variable.

• The kinetic theory of matter states that all particles of matter are in constant motion.

• There are forces of attraction among the particlesin all matter.

• The constant motion of particles in a gas allows agas to fill a container of any shape or size.

• A liquid takes the shape of its container becauseparticles in a liquid can flow to new locations. Thevolume of a liquid is constant because forces ofattraction keep the particles close together.

• Solids have a definite volume and shape becauseparticles in a solid vibrate around fixed locations.

Vocabulary

solid, p. 69; liquid, p. 69; gas, p. 70; kinetic energy, p. 71

3.2 The Gas Laws

Key Concepts

• Collisions between particles of a gas and the wallsof the container cause the pressure in a closedcontainer of gas.

• Factors that affect the pressure of an enclosed gasare its temperature, its volume, and the number ofits particles.

• Raising the temperature of a gas will increase itspressure if the volume of the gas and the numberof particles are constant.

• Reducing the volume of a gas increases its pressureif the temperature of the gas and the number ofparticles are constant.

• Increasing the number of particles will increase thepressure of a gas if the temperature and thevolume are constant.

• The combined gas law can be expressed as

�

Vocabulary

pressure, p. 75; absolute zero, p. 78; Charles’s law, p. 78; Boyle’s law, p. 79

P2V2T2

P1V1T1

3.3 Phase Changes

Key Concepts

• Melting, freezing, vaporization, condensation,sublimation, and deposition are six common phase changes.

• The temperature of a substance does not changeduring a phase change.

• Energy is either absorbed or released during aphase change.

• The arrangement of molecules in water becomesless orderly as water melts, and more orderly aswater freezes.

• Evaporation takes place at the surface of aliquid and occurs at temperatures below theboiling point.

Vocabulary

phase change, p. 84; endothermic, p. 86; heat of fusion, p. 86; exothermic, p. 86; vaporization, p. 88; heat of vaporization, p. 88;evaporation, p. 89; vapor pressure, p. 89;condensation, p. 90; sublimation, p. 91; deposition, p. 91;

Web Diagram Use information from the chapter tocomplete the web diagram on phase changes.

Thinking Visually

Phasechanges

a. ? b. ?

Deposition

Exothermic

Sublimation

Melting c. ? d. ?

94 Chapter 3

Study Guide

Study TipStudy With a PartnerOn occasion, study with a friend. Quizeach other, compare notes from classlectures, go over homework answers,and discuss concepts that you need helpwith understanding.

Thinking Visuallya. and b. Condensation, freezingc. Endothermicd. Vaporization

Assessment

If your class subscribes to the Interactive Textbook, your students can go online to access aninteractive version of the StudentEdition and a self-test.

Reviewing Content1. b 2. c 3. c4. b 5. a 6. d7. c 8. b 9. c

10. a

Chapter 3

Print• Chapter and Unit Tests, Chapter 3

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Chapter Resources

States of Matter 95

CHAPTER

3 Assessment

Choose the letter that best answers the question orcompletes the statement.

1. Which state of matter has a definite volume but avariable shape?

a. solid b. liquid c. gas d. vapor

2. In which state(s) of matter can materials take theshape of their containers?

a. solid and liquid b. solid and gasc. liquid and gas d. liquid only

3. Which statement is true about the atoms inhelium gas?

a. They travel in circular paths.b. They have strong attractions to

one another.c. They are not closely packed.d. They are arranged in an orderly pattern.

4. If the speed of an object increases, its kinetic energy

a. decreases. b. increases.c. stays the same. d. is unpredictable.

5. The SI unit of pressure is thea. pascal. b. newton.c. square meter. d. psi.

6. Increasing which variable would decrease thepressure of a contained gas?

a. temperature b. number of particles c. boiling point d. volume

7. Boyle’s law relates pressure and a. temperature. b. number of particles.c. volume. d. mass.

8. Which of the following changes is exothermic?a. evaporation b. freezingc. boiling d. sublimation

9. The phase change that is the reverse ofvaporization is

a. freezing. b. melting.c. condensation. d. evaporation.

10. Which of these phase changes does NOT involvechanging a liquid into a gas?

a. sublimation b. vaporization c. evaporation d. boiling

Reviewing Content

11. Provide an example of each of the three states ofmatter that exist at room temperature.

12. Compare and contrast liquid water and ice in termsof how definite their shapes and volumes are.

13. What three assumptions about particles in a gasare made by the kinetic theory?

14. Using the kinetic theory, explain why a liquid hasa definite volume but a gas does not.

15. How do the way that atoms are arranged inliquid mercury and solid copper affect themovement of mercury and copper atoms?

16. Using the kinetic theory, explain what causes gas pressure.

17. What three factors affect the pressure of a gas in a closed container?

18. If a piston moves downward in a cylinder, whathappens to the volume and pressure of the gas inthe cylinder? The temperature remains constant.

19. What happens to the speed of the particles insidean air-filled balloon if the temperature of theballoon increases?

20. Using the kinetic theory, explain why the pressureof a gas increases when its temperature increases.

21. How are the pressure and volume of a gas related?

22. How does an endothermic phase change differfrom an exothermic phase change?

23. Compare the vapor pressure of water at 10°Cwith its vapor pressure at 50°C.

24. Explain why water has a different boiling point at an elevation of 3000 meters than it does at sea level.

Understanding Concepts

Interactive Textbook withassessment at PHSchool.com

Assessment (continued)

Understanding Concepts11. Examples might include solidcopper, liquid water, and the heliuminside a balloon as a gas.12. Both liquid water and ice have adefinite volume. Ice has a definite shape, but liquid water does not.13. The particles are in constant,random motion. The motion of oneparticle is unaffected by the motion of other particles unless the particlescollide. Under ordinary conditions,forces of attraction between particlescan be ignored. 14. The attractions between theparticles in a liquid are strong enough to keep the particles close together.Without any significant attractionsbetween particles in a gas, the particlesare free to expand into any volume thatis available. 15. The atoms in copper vibrate aroundfixed positions. The atoms in mercurycan flow past one another. 16. Gas pressure is caused by collisionsof atoms with their containers.17. Temperature, volume, and thenumber of particles 18. The volume decreases and thepressure increases.19. The particles in the air move faster,on average, when the temperatureincreases because they have morekinetic energy.20. When the temperature of a gasincreases, the particles have greaterkinetic energy, on average, and movefaster. Thus, atoms hit the walls of thecontainer more often and with greaterforce, causing the pressure to increase.21. The volume of a gas is inverselyproportional to its pressure.22. During an endothermic phasechange, energy is absorbed by thesystem. During an exothermic phasechange, energy is released by thesystem.23. The vapor pressure of water isgreater at 50°C than it is at 10°C.24. Water boils when its vapor pressurebecomes equal to atmospheric pressure.At 3000 m, the atmospheric pressure islower than it is at sea level. Thus, vaporpressure equals atmospheric pressure ata lower temperature, and water boils ata lower temperature.

States of Matter 95

Homework GuideSection

3.13.23.2

Questions1–4, 11–16, 335–7, 17–21, 27–28, 30–32, 35–368–10, 22–26, 29, 34, 37

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96 Chapter 3

CHAPTER

3 Assessment (continued)

25. Classifying If you take a helium balloon frominside a warm house to outside on a snowy day,what will happen to the balloon? Could youclassify this change as a phase change? Explainyour answer.

26. Comparing and Contrasting Compare themelting and freezing of water in terms of (a) thetemperature at which these processes take placeand (b) how energy is involved in these processes.

Use the graphs to answer Questions 27–29.

27. Using Graphs Which graph represents whathappens to the pressure in a tire as air is addedto the tire? Assume the temperature of the gasis constant.

28. Using Graphs Which graph represents whathappens to the pressure in an aerosol can if thecan is heated?

29. Applying Concepts Which graph representstemperature versus time during a phase change?

30. Making Generalizations The pressure of a gasis directly proportional to its temperature in kelvins.Using P1, P2, T1, and T2, write a mathematicalequation that expresses this relationship.

31. Calculating An automobile tire has a pressureof 325 kPa when the temperature is 10°C. If thetemperature of the tire rises to 50°C and itsvolume is constant, what is the new pressure?

32. Calculating A gas sample occupies 4.2 L at apressure of 101 kPa. What volume will it occupyif the pressure is increased to 235 kPa?

Math Skills

Critical Thinking

33. Using Models If there is a gas leak in thebasement of a building, you will soon notice anodor throughout the house. However, if there is awater leak in the basement, you will need to goto the basement to detect the leak. Use thekinetic theory to explain the differences.

34. Inferring A student examines a thermometerplaced in a can containing a substance that isbeing heated. The temperature remains the samefor several minutes, and then it starts to rise.Without looking in the can, how does the studentknow what is occurring in the can?

35. Relating Cause and Effect In Earth’satmosphere, pressure and temperature bothdecrease as altitude increases. Weather balloonsexpand as they rise. Which has more effect on theweather balloon, the decrease in pressure or thedecrease in temperature? Explain your answer.

36. Drawing Conclusions In a car engine, air andgasoline vapors are mixed in a cylinder. A pistonis pushed into the cylinder before a spark ignitesthe mixture of gases. When the piston is pushedinto the cylinder, what happens to the pressureof the gases in the cylinder?

37. Writing in Science Unpopped popcorn kernelscontain a small amount of water. Use what youknow about vaporization and how gases behaveto explain why popcorn pops when it is heated.

Making a Poster The gas laws have many practicalapplications in cooking. Make a poster, includingdiagrams, that shows how two factors that affect gasesaffect cooking. Examples might include explainingwhy cakes rise while baking or why some recipesspecify high-altitude temperatures and cooking times.

Performance-Based Assessment

Concepts in Action

A. C. B.

For: Self-grading assessment

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Web Code: cca-1030

A B C

96 Chapter 3

Critical Thinking25. A balloon that is flexible will shrink.This observed change is not a phasechange because helium is a gas beforeand after the change.26. (a) Water melts and freezes at thesame temperature. (b) Melting is anendothermic process. Freezing is anexothermic process.27. Graph A 28. Graph A29. Graph C

Math Skills30. P1/P2 � T1/T2 or P1/T1 � P2/T231. 371 kPa 32. 1.8 L

Concepts in Action33. There is almost no attractionbetween particles in a gas. They willquickly spread throughout the building.Because particles in a liquid stronglyattract one another, they remain closetogether and don’t spread throughoutthe building (unless the water quantityis large and there is no drain).34. Because energy is being added butno increase in temperature occurs, aphase change is occurring in the can. 35. A decrease in pressure causes anincrease in volume. A decrease intemperature causes a decrease involume. Because the volume of theballoon increases, the decrease inpressure must affect the balloon morethan the decrease in temperature.36. The pressure increases. 37. Heating causes the water to vaporize.With continued heating, the pressure ofthe vapor increases because the volumeof the confined vapor is constant. Eventu-ally, the increased pressure causes thekernel to burst open.

Chapter 3

Performance-Based AssessmentPossible poster topics: Gas bubbles formed incake batter increase in volume when the batter isheated, causing the cake to rise. Cake mixes oftenhave instructions for baking at higher altitudesbecause the boiling point of water decreases athigher elevations. In a pressure cooker, the volumeof air is constant. Heating the air increases both itstemperature and pressure, and the food cooks in ashorter amount of time.

Your students can independentlytest their knowledge of the chapterand print out their test results foryour files.

States of Matter 97

Standardized Test Prep

Choose the letter that best answers the question orcompletes the statement.

1. A material can be classified as a liquid if(A) it has a definite shape and a

definite volume.(B) it has a definite shape and a

variable volume.(C) it has a variable shape and a

definite volume.(D) it has a variable shape and a

variable volume.(E) its particles vibrate around fixed locations.

2. Which statement best explains what must takeplace for water to boil?(A) The water releases energy to its

surroundings.(B) Bubbles rise to the surface of the water.(C) The vapor pressure of the water becomes

equal to atmospheric pressure.(D) Molecules at the surface of the water

overcome the attractions of neighboringmolecules.

(E) The temperature of the water increases.

3. Condensation is the phase change in which asubstance changes from(A) a solid to a gas.(B) a solid to a liquid.(C) a liquid to a solid.(D) a liquid to a gas.(E) a gas to a liquid.

4. Which of these statements about an enclosedgas is true? (Assume all quantities are constantexcept the two variables described in eachstatement.)(A) Raising the temperature of a gas will

increase its pressure.(B) Increasing the volume of a gas will increase

its pressure.(C) Reducing the number of particles of a gas

will increase its pressure.(D) The volume of a gas is inversely

proportional to its temperature in kelvins.(E) The volume of a gas is directly proportional

to its pressure.

Use the illustration to answer Question 5. Assume thatthe number of particles of gas in container A equals thenumber of particles of gas in container B.

5. If the temperature is constant, the pressure incontainer B is(A) one half the pressure in container A.(B) twice the pressure in container A.(C) equal to the pressure in container A. (D) five times the pressure in container A.(E) one fifth the pressure in container A.

6. During an endothermic phase change,(A) the temperature of a substance rises.(B) the temperature of a substance decreases.(C) energy is transferred from a substance to

its surroundings.(D) a substance absorbs energy from

its surroundings.(E) there is no transfer of energy.

Test-Taking Tip

Watch For QualifiersThe words best and least are examples of quali-fiers. If a question contains a qualifier, more thanone answer will contain correct information.However, only one answer will be complete andcorrect for the question asked. Look at the ques-tion below. Eliminate any answers that are clearlyincorrect. Then choose the remaining answer thatoffers the best explanation for the question asked.

Choose the best explanation for why oneparticle in a gas does not affect other particlesin a gas unless the particles collide.(A) Particles in a gas are constantly moving.(B) All the particles in a gas have the same

kinetic energy.(C) There are no forces of attraction among

particles in a gas. (D) There are billions of particles in a small

sample of a gas.(E) Particles in a gas are relatively far apart.

(Answer: E)

1.0 L

0.5 L

A B

Standardized Test Prep1. C 2. C 3. E4. A 5. B 6. D

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3.1 Solids, Liquids, and Gases

Reading Strategy Comparing and Contrasting Copy thediagram. As you read, replace each letter withone of these phrases: definite volume, definiteshape, variable volume, or variable shape.

Key ConceptsHow can shape andvolume be used toclassify materials?

How can kinetic theoryand forces of attractionbe used to explain thebehavior of gases, liquids,and solids?

Vocabulary◆ solid◆ liquid◆ gas◆ kinetic energy

Do you recognize the object in Figure 1? It is a carpenter’s level. Alevel can be used to see whether a surface is perfectly horizontal. Thelevel has one or more transparent tubes inside a metal or woodenframe. Inside each tube is a clear liquid, such as alcohol, and an airbubble. When a carpenter places the level on a surface that is perfectlyhorizontal, the air bubble stays in the middle of the horizontal tube.The bubble moves to the high end of the tube if the surface is slanted.

The metal, alcohol, and air in a carpenter’s level represent threestates of matter. At room temperature, most metals are solids, alcoholis a liquid, and air is a gas. In this chapter, you will learn why theappearance and behavior of solids, liquids, and gases are different.

Describing the States of MatterIf you were asked to classify some materials as solids, liquids, or gases,you would probably find the task fairly easy. But could you describewhat method you used to classify the materials? You might noticethat some materials have a definite shape and volume and somematerials do not. Materials can be classified as solids, liquids, orgases based on whether their shapes and volumes are definite orvariable. Shape and volume are clues to how the particles within amaterial are arranged.

Figure 1 Carpenters use a levelto find out if a surface is perfectlyhorizontal. In the level shown,three clear plastic tubes are setinto an aluminum frame. Eachtube contains a liquid and a gas.Classifying What property couldyou use to distinguish the liquidor gas from the solids in a level?

LiquidSolid Gas

a. ? b. ? c. ? d. ?

68 Chapter 3

68 Chapter 3

FOCUS

Objectives3.1.1 Describe the five states of

matter.3.1.2 Classify materials as solids,

liquids, or gases.3.1.3 Explain the behavior of

gases, liquids, and solids, using kinetic theory.

Build VocabularyWord Origins Explain to students that a Flemish chemist, Jan Baptista van Helmont (1577–1644), coined theword gas. Its origin is the Greek wordkhaos. Point out that the English wordchaos refers to a disordered state. Relate this definition to the relativedisorder of gases.

Reading Strategya. Definite shape b. Definite volume c. Variable shape d. Variable volume

INSTRUCT

Describing the States of MatterUse VisualsFigure 1 Have students look at themagnified portion. Ask, Why is the airbubble above the liquid in the tube?(Air is less dense than the liquid.) Whenmight the tube in the middle of thelevel be used? (To see whether a shelf orcounter is perfectly horizontal) Whenmight the tube on the right be used?(To see whether a wall or doorframe isperfectly vertical) If possible, bring inlevels for students to observe and use.Visual

L1

2

L2

L2

Reading Focus

1

Section 3.1

Print• Laboratory Manual, Investigation 3B • Reading and Study Workbook With

Math Support, Section 3.1• Math Skills and Problem Solving

Workbook, Section 3.1•Transparencies, Chapter Pretest and

Section 3.1

Technology• Interactive Textbook, Section 3.1• Presentation Pro CD-ROM, Chapter Pretest

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Section Resources

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Solids Think about these familiar objects: a pencil, a quarter, abook, and a cafeteria tray. What do these four objects have incommon? They all have a recognizable shape and they all takeup a certain amount of space. The materials in these objectsare all in the solid state. Solid is the state of matter in whichmaterials have a definite shape and a definite volume.

The term definite means that the shape and volume ofa pencil won’t change as you move the pencil from a deskdrawer to a pencil case to a backpack. Changing the con-tainer doesn’t change the shape or volume of a solid.However, the term definite doesn’t mean that the shape orvolume can never change. After all, you can change the shape ofa pencil by sharpening it. You can change the shape of a copperwire by bending the wire.

Figure 2 shows the arrangement of atoms in a copper wire. Thecopper atoms are packed close together and are arranged in a regularpattern. Almost all solids have some type of orderly arrangement ofparticles at the atomic level.

Liquids How good are you at estimating whether the juice remain-ing in an almost-empty bottle will fit in a glass? If your estimate is notaccurate, you will run out of space in the glass before you run out ofjuice in the bottle.

Appearances can be deceiving. Imagine a narrow glass and a widebottle side by side. Each contains exactly 350 milliliters of juice (aboutthree quarters of a pint). There will seem to be more juice in the glassbecause the juice rises almost to the rim of the glass. There will seemto be less juice in the bottle because the juice forms a shallow layer.What can you learn about liquids from this comparison?

A liquid always has the same shape as its container and can bepoured from one container to another. Liquid is the state of matter inwhich a material has a definite volume but not a definite shape.

Mercury exists as a liquid at room temperature.The drawing in Figure 3 shows the arrangement ofatoms in liquid mercury. Compare this arrange-ment to the arrangement of copper atoms inFigure 2. The mercury atoms are close togetherbut their arrangement is more random than thearrangement of atoms in copper.

Figure 2 Samples of solid copperhave definite volume. Copperatoms are packed close togetherin an orderly arrangement.

States of Matter 69

Figure 3 At room temperature, mercury is a liquid.Drops of mercury on a flat, clean surface have a roundshape. Mercury in a container has the same shape as itscontainer. Comparing and Contrasting Compare thearrangement of atoms in copper and mercury.

Comparing Liquid Volume

Purpose Students observe that it isdifficult to compare the volume of liquidsin different containers because liquidstake the shape of their containers.

Materials 3 glass jars or bottles withlids, each having a noticeably differentdiameter but about the same volume;graduated cylinder; water

Advance Prep Before class, use agraduated cylinder to add the sameamount of water to each of the threecontainers. Pick a volume that willalmost fill the narrowest container. To avoid evaporation, replace the lids on the containers.

Procedure Have students predictwhich container has the largest volumeof water. Have volunteers use graduatedcylinders to measure the amount ofwater in each container.

Expected Outcome If students’ predic-tions are influenced by the height of theliquids in the containers, they will predictthat the container with the narrowestdiameter has the greatest volume.Visual

Build Reading LiteracyRelate Text and Visuals Refer to page 190D in Chapter 7, which provides the guidelines for relating text and visuals.

Have students compare the drawings of a solid and a liquid in Figures 2 and 3 tothe definitions for these states of matter. Visual, Portfolio

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States of Matter 69

Customize for English Language Learners

Think-Pair-ShareHave students work in pairs to make a tabledescribing solids, liquids, and gases. Remindstudents that they need to include in theirdescriptions information about shape, volume,and the arrangement of particles. An exampleof such a table would have Solids, Liquids, and

Gases as column heads and Shape, Volume,and Arrangement of Particles as row heads.Students should title their tables States ofMatter. Suggest that students list commonexamples of each state. Strengthen languageskills by having students present their tables to the class.

Answer to . . .

Figure 1 The liquid and gas havevariable shapes.

Figure 3 In both copper andmercury, the atoms are close together,but the arrangement of atoms inmercury is less orderly (more random).

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70 Chapter 3

Gases If you were asked to name a gas, what would you say? Air,which is a mixture of gases, is probably the most obvious example. Youmight also mention natural gas, which is used as a fuel for heatinghomes. Gas is the state of matter in which a material has neither a def-

inite shape nor a definite volume. (The adjective form of the word gasis gaseous (GAS e us), as in gaseous state.) A gas takes the shape and

volume of its container.The balloons in Figure 4 are filled with helium, a colorless

gas that is less dense than air. Two of the balloons are teardrop-shaped and two are disk-shaped. The “shape” of the heliumin a balloon is the same as the shape of the balloon itself. Thevolume of the helium in a balloon is equal to the volume ofthe balloon.

The helium atoms in a balloon are not arranged in aregular pattern, as shown in the drawing in Figure 4.

They are at random locations throughout the bal-loon. There is more space between two heliumatoms in a balloon than between two neighboringatoms in solid copper or liquid mercury.

Because of the space among helium atoms, alarge amount of helium can be compressed into a

metal cylinder. When helium flows from the cylinderinto a balloon, the helium atoms spread out. If 200 bal-

loons are filled from a single cylinder, the total volume of theballoons will be much larger than the volume of the cylinder.

Other States of Matter On Earth, almost all matter exists ina solid, liquid, or gaseous state. But ninety-nine percent of all thematter that can be observed in the universe exists in a state that is notas common on Earth. At extremely high temperatures, such as thosefound on the sun or other stars, matter exists as plasma. You will readmore about the properties of plasmas in Chapter 10.

In the 1920s Satyendra Bose, a physicist from India, wrote a paperabout the behavior of light. After Albert Einstein read the paper, herealized that the behavior described could apply to matter under cer-tain conditions. Einstein made a bold prediction. He predicted that afifth state of matter would exist at extremely low temperatures. At tem-peratures near �273°C, groups of atoms would behave as though theywere a single particle. In 1995, scientists produced this fifth state ofmatter, which is called a Bose-Einstein condensate (or BEC). It behavedas Einstein had predicted decades before.

How can atoms behave at temperaturesnear _273°C?

Figure 4 Helium gas takes thevolume and shape of its container.Observing Describe the shape ofthe helium in the blue balloon.

70 Chapter 3

Use VisualsFigure 4 To help students distinguish a visual model of atoms from actualatoms, point out that the pink spheresrepresent helium atoms in a balloon. Ask, Do the size and color of thespheres represent the actual size and color of helium atoms? (No, helium atoms are too small to see andhelium is a colorless gas.) Tell students that the actual distance between heliumatoms in a balloon is about 10 times thediameter of a helium atom. Have studentsconsider why illustrations cannotaccurately represent such distances.Visual, Logical

FYIIn this chapter, plasma is not defined asan ionized gas because students are notintroduced to ions until Chapter 6.

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Section 3.1 (continued)

Bose-Einstein Condensate In 1995,physicists at the University of Colorado atBoulder were the first to produce a BEC. The team of scientists, which included EricCornell and Carl Wieman, used lasers andmagnets to cool about 2000 rubidium atomsto 20 billionths of a degree above absolutezero (�273.15°C). The rubidium atoms formeda tiny, almost stationary ball, which looked likea cherry pit with a diameter of 20 microns.

In 1997, Steven Chu, William Phillips, andClaude Cohen-Tannnoudji shared the NobelPrize for Physics for their independent workusing lasers to cool atoms. In 1985, Chu andhis team had produced “optical molasses,” aneffect in which the movement of atoms wasabout one kilometers per hour instead of theexpected 4000 kilometers per hour. At thatspeed the temperature of the sample was close to absolute zero.

Facts and Figures

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Kinetic TheoryWhy, under ordinary conditions, is copper a solid, mercury a liquid,and helium a gas? To begin to answer that question, you need to knowsomething about kinetic energy. An object that is moving has kineticenergy. The word kinetic comes from a Greek word meaning “to move.”Kinetic energy is the energy an object has due to its motion.

The faster an object moves, the greater its kinetic energy is. A ballthrown at 85 miles (137 kilometers) per hour by the pitcher in Figure 5has more kinetic energy than a ball thrown at 78 miles (125 kilometers)per hour. When a baseball is thrown, a batter can see that it is moving.But the batter cannot see that there is also motion occurring withinthe baseball. According to the kinetic theory ofmatter, particles inside the solid baseball are moving.Particles in the air that the baseball travels throughare moving too.

The kinetic theory of matter says that allparticles of matter are in constant motion. Thetheory was developed in the mid-1800s to explainthe behavior of gases. It can also help to explain thebehavior of liquids and solids.

Why Was Mercury Used inThermometers?

Until recently, mercury thermometers were used inhomes and schools. When a thermometer broke,people were exposed to mercury. When brokenthermometers were thrown away, they ended upin landfills. Mercury is a toxic substance that canharm humans and other organisms. Schools nolonger use mercury thermometers and people areencouraged to replace their fever thermometers.

So why did people continue to use mercurythermometers long after they knew the dangers ofmercury? Look at the data table. It lists somedensities over a temperature range from 0°C to150°C. The temperatures are given at 30-degreeintervals.

1. Using Tables How does the density ofmercury change as the temperature increases?

2. Relating Cause and Effect How does achange in density affect the volume of amercury sample?

Temperature(�C)

0

30

60

90

120

150

Density(g/mL)

13.60

13.52

13.45

13.38

13.30

13.23

Volume of One Gram(mL)

0.07356

0.07396

0.07436

0.07476

0.07517

0.07558

Density of Mercury

Figure 5 The kinetic energy of abaseball depends on the speed atwhich the pitcher throws the ball.

3. Calculating If a thermometer contained agram of mercury, how much would the volumeof the mercury change when the temperaturerose from 0°C to 30°C? From 30°C to 60°C?From 60°C to 90°C? From 90°C to 120°C?

4. Drawing Conclusions Why was mercury abetter choice than water for the liquid in athermometer? (Hint: Between 0°C and 30°C,the volume of a gram of water changes by0.0042 mL. Between 30°C and 60°C, thevolume changes by 0.0127 mL. Between 60°Cand 90°C, the volume changes by 0.0188 mL.)

5. Inferring Why is the mercury in athermometer stored in a narrow tube?

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Why Was Mercury Used in Thermometers?Answers1. The density decreases.2. As the density decreases, the volume increases.3. 0.00040 mL; 0.00040 mL; 0.00040 mL; 0.00041 mL4. Unlike with water, the change involume for mercury is almost identicalfor each interval. (The expansion islinear.) Thus, the interval spacingbetween degree marks is consistent formercury. (In addition, the liquid rangefor mercury is broader—from –38.9°C to 356.7°C.)5. With such a small change in volumeper degree, the mercury must be in anarrow tube for the difference in heightto be observed and measured.

For Extra HelpDisplay a copy of the data table on theboard. If students are having troubleanswering Question 4, have a studentrecord the incremental change involume (calculated for Question 3) and change in temperature from row to row. This step should make it easierfor students to see that the almostconstant change in volume correspondsto a constant temperature interval. Logical

Kinetic Theory FYIThe kinetic energy of an object is alsoaffected by its mass. The greater themass of an object, the greater its kineticenergy is. (This effect of mass and speed on kinetic energy is discussed in Section 15.1.)

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States of Matter 71

Mercury Thermometer Daniel Fahrenheitinvented the alcohol thermometer in 1709and the mercury thermometer in 1714. Hechose mercury because it remains a liquid over a wider range of temperatures than does water. The expansion rate of mercury is fairly uniform, mercury does not adhere to glass, and its color makes it easy to read.

Inhalation of mercury vapor can damagethe nervous system and the respiratory system.

To prevent mercury vapor from being inhaledwhen thermometers break, the EnvironmentalProtection Agency, along with state and local agencies, has encouraged consumers to replace mercury fever thermometers.Alternatives to mercury thermometers includedigital thermometers that use a change in the resistance in a thermoresistor andthermometers with sensors that detectinfrared radiation.

Facts and Figures

Answer to . . .

Figure 4 The helium in the blueballoon is star-shaped.

Groups of atoms canbehave as though they

were a single particle.

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72 Chapter 3

Explaining the Behavior of GasesYou can compare the motion of the particles in a gas to the movementof balls during a game of billiards. When a cue strikes a billiard ball, asshown in Figure 6, the ball moves in a straight line until it strikes theside of the billiard table or another ball. When a moving ball strikes aball at rest, the first ball slows down and the second ball begins tomove. Kinetic energy is transferred during those collisions.

Motion in Gases Unlike billiard balls, the particles in a gas arenever at rest. At room temperature, the average speed of the particlesin a sample of gas is about 1600 kilometers per hour. The use of theterm average is a clue that not all particles are moving at the samespeed. Some are moving faster than the average speed and some aremoving slower than the average speed.

Figure 7 shows the possible paths of two helium atoms in a con-tainer of helium gas. Notice that each atom moves in a straight lineuntil it collides with the other atom or with a wall of the container.During a collision, one atom may lose kinetic energy and slow downwhile the other atom gains kinetic energy and speeds up. However, thetotal kinetic energy of the atoms remains the same.

The diagram in Figure 7 does not accurately compare the volumesof the atoms and the container. The volume of a helium atom isextremely small compared to the volume of its container. If there werea billion times a trillion helium atoms in a liter bottle, there would stillbe a large amount of space in the bottle.

Between collisions, why doesn’t one particle in a gas affect the otherparticles in the gas? There are forces of attraction among theparticles in all matter. If the particles are apart and moving fast, as ina gas, the attractions are too weak to have an effect. Under ordinaryconditions, scientists can ignore the forces of attraction in a gas.

Figure 6 This photograph ofbilliard balls was taken just afterthe cue struck the white ball,which began to move. The whiteball moved in a straight line untilit collided with the dark blue ball.The collision caused the dark blueball to start moving. The motionof billiard balls can be comparedto the motion of particles in a gas.

Figure 7 A helium atom travelsin a straight line until it collideswith another helium atom or theside of its container. Relating Cause and EffectWhat can happen to the kineticenergy of two helium atomswhen the atoms collide?

72 Chapter 3

Explaining theBehavior of Gases

Detecting the Motion of a Gas

Purpose Students infer that particles in gases are in constant motion.

Materials spray can of air freshener, 3 stopwatches

Procedure Spray the air freshener at a distant corner of the room. Havestudents located in various parts of theroom time how long it takes before they smell the gas. (The mist from thespray will evaporate.) Ask students toexplain the results.

Expected Outcome Students willdetect odor several moments after theair freshener is sprayed. Students shouldexplain that they could smell the airfreshener because the particles in a gasare in constant, random motion. Thatmotion carried particles from the cornerof the room to the students’ locations. Kinesthetic, Logical

Use VisualsFigures 6 and 7 Have studentscompare the models of collisions shownin Figures 6 and 7. Ask, How are thepaths of billiard balls and helium atomsthe same? (The paths of both are straightlines.) How is the motion of billiard ballsdifferent from the motion of heliumatoms? (The motion of billiard balls is notconstant or random.) What is a weaknessof the model of helium atoms shown in Figure 7? (There are only two atoms torepresent the billions of atoms that would be in such a jar.)Visual

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Section 3.1 (continued)

Mean Free Path The distance a particle of gastravels between collisions is called its mean freepath. This distance varies with temperature andpressure. At 1 atmosphere of pressure and 25°C,the mean free path for a hydrogen molecule is12.6 � 10�8 meters. For a nitrogen molecule, it is 6.76 � 10�8 meters. At 1 atmosphere of

pressure and 25°C, a hydrogen molecule will collide with another molecule about 7.1 � 1011 times per second, while a nitrogenmolecule will collide with another moleculeabout 1.42 � 1010 times per second. Theshorter the mean free path is, the greater thenumber of collisions per second.

Facts and Figures

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Figure 8 Particles in a liquidbehave like students movingthrough a crowded hallway.

Kinetic Theory of Gases The kinetic theory explains the gen-eral properties of a gas. The constant motion of particles in a gasallows a gas to fill a container of any shape or size. Think about air ina tire. The walls of the tire keep the air contained. What if there is a holein the tire? Because the particles in the air are in constant motion, someof the particles would travel to the hole and move out of the tire. Thekinetic theory as applied to gases has three main points.

■ Particles in a gas are in constant, random motion.

■ The motion of one particle is unaffected by the motion of otherparticles unless the particles collide.

■ Forces of attraction among particles in a gas can be ignored underordinary conditions.

Explaining the Behavior of Liquids The particles in liquids also have kinetic energy. So why does a liquidsuch as mercury have a definite volume at room temperature insteadof expanding to fill its container? The average speed of a mercury atomis much slower than the average speed of a helium atom at the sametemperature. A mercury atom has about 50 times the mass of a heliumatom. This greater mass is only partly responsible for the slower speed.What other factor is responsible?

The particles in a liquid are more closely packed than the particles ina gas. Therefore, attractions between the particles in a liquid do affect themovement of the particles. A mercury atom in liquid mercury is like astudent in the crowded hallway in Figure 8. The student’s path may beblocked by students moving in the other direc-tion. The student’s ability to move is affected byinteractions with other students.

In a liquid, there is a kind of tug of warbetween the constant motion of particles andthe attractions among particles. This tug ofwar explains the general behavior of liquids.

A liquid takes the shape of its containerbecause particles in a liquid can flow to newlocations. The volume of a liquid is constantbecause forces of attraction keep the particlesclose together. Because forces of attractionlimit the motion of particles in a liquid, theparticles in a liquid cannot spread out and filla container.

Describe the motion of particles in a gas.

73

For: Links on kinetic theory

Visit: www.SciLinks.org

Web Code: ccn-1031

For: Activity on mercury in the enviroment

Visit: PHSchool.com

Web Code: ccc-1031

Explaining theBehavior of LiquidsBuild Science SkillsUsing Analogies Have students think of analogies for the motion of particles in a liquid other than the analogy shown in Figure 8. Possible answers includedancers on a dance floor or bumper carsat an amusement park. Be sure studentsunderstand that the objects represent-ing particles in the analogy should be ina confined space.Logical

Students may think that the particles in gases have more kinetic energy thanthe particles in liquids or solids. Studentsare confusing an increase in the abilityof particles to move freely with anincrease in average speed. Challengethis misconception by explaining thatthe particles in all substances at a giventemperature have, on average, similaramounts of kinetic energy. Ask, Whydon’t particles in a solid move asfreely as particles in a gas at roomtemperature? (Strong forces of attractionamong particles in the solid keep theparticles vibrating around fixed locationswithin the solid.) Logical

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States of Matter 73

Download a worksheet on kinetictheory for students to complete,and find additional teacher supportfrom NSTA SciLinks.

Answer to . . .

Figure 7 One atom may gain kineticenergy and speed up while the otheratom loses kinetic energy and slowsdown.

Particles in a gas are in constant,

random motion.

IPLS

Find links to additional activitiesand have students monitorphenomena that affect Earthand its residents.

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74 Chapter 3

Section 3.1 Assessment

Reviewing Concepts1. How are shape and volume used to

classify solids, liquids, and gases?

2. What does the kinetic theory say aboutthe motion of atoms?

3. How is a gas able to fill a container of anysize or shape?

4. Use kinetic theory and attractive forces toexplain why a liquid has a definite volume anda shape that can vary.

5. Explain why a solid has a definite shapeand volume.

6. How does the arrangement of atoms in mostsolids differ from the arrangement of atoms ina liquid?

Critical Thinking 7. Using Analogies Explain how the behavior

of popcorn in a popcorn popper can be usedas an analogy for the motion of gas particles.

8. Applying Concepts A hazardous chemical isleaking from a tank truck. Rescue workers needto evacuate people who live near the accident.Why are more people likely to be affected ifthe chemical is a gas, rather than a liquid?

Explaining the Behavior of SolidsYou might compare the particles in a solid to a polite audience in amovie theater. While the movie is running, people stay in their seats.Although people move around in their seats, as shown in Figure 9, eachperson remains in essentially the same location during the movie. Theyhave “fixed” locations in a total volume that does not change.

Solids have a definite volume and shape because particles ina solid vibrate around fixed locations. Vibration is a repetitive back-and-forth motion. Look back at the orderly arrangement of copperatoms in Figure 2. Strong attractions among the copper atoms restricttheir motion and keep each atom in a fixed location relative to itsneighbors. Each atom vibrates around its location but it does notexchange places with a neighboring atom.

Viscosity Review the description of vis-cosity in Section 2.2. Use the tug of warbetween forces of attraction and kineticenergy to explain differences in viscosityamong liquids at the same temperature.

Figure 9 These photographs ofan audience in a movie theaterwere taken at different times onthe same day. The behavior of theaudience can be compared to thebehavior of particles in a solid.Observing What stayed thesame and what changed betweenthe photographs?

74 Chapter 3

Explaining theBehavior of SolidsBuild Science SkillsUsing Models Fill a clear plastic box or tray with enough marbles to fill thebottom of the box. Gently move thebox back and forth. Ask, What state ofmatter does this model represent?(Solid) How are the particles in a solidlike the marbles in this model? (Boththe marbles and the particles in a solid are in fixed locations. They can only moveback and forth.) The marbles do notmove until the box is shaken. How welldoes this part of the model representthe behavior of particles in a solid?(Not well, because particles in a solid areconstantly moving.) Visual

ASSESSEvaluate UnderstandingHave each student write a paragraphexplaining how kinetic theory can beused to explain the general characteristicsof solids, liquids, and gases.

ReteachReview the properties of solids, liquids,and gases. Use Figure 1 to encouragestudents to think of practical applicationsin which the state of matter is important.For example, molten metals can beshaped in a mold, but a metal must be solid to be shaped by hammering.

In a liquid, there is a tug of war betweenthe motion of the particles and attrac-tions among particles. With liquids atthe same temperature, the decidingfactor would be the strength of theattractive forces. An increase in theseforces would decrease a liquid’s ability to flow and increase its viscosity.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 3.1.

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3

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Section 3.1 (continued)

5. The particles in a solid vibrate around fixed locations.6. The atoms in most solids have a moreorderly arrangement than the atoms in liquids,which are not restricted to fixed locations. 7. While popping occurs, the motion of theindividual popcorn kernels is random andfairly continuous.8. The particles of a gas have greater freedomof movement and will reach a wider area more quickly.

Section 3.1 Assessment

1. Materials can be classified as solids, liquids,or gases based on whether their shapes andvolumes are definite or variable.2. All particles of matter are in constantmotion. 3. The constant motion of gas particles allowsa gas to fill a container of any shape and size.4. Particles in a liquid can flow to newlocations, but forces of attraction keep theparticles close together.

Answer to . . .

Figure 9 People remain in the sameseats, but the positions of their bodieschange.

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3.2 The Gas Laws

Reading StrategyIdentifying Cause and Effect Copy thediagram. As you read, identify the variablesthat affect gas pressure.

Key ConceptsWhat causes gas pressurein a closed container?

What factors affect gaspressure?

How are the temperature,volume, and pressure of agas related?

Vocabulary◆ pressure ◆ absolute zero◆ Charles’s law◆ Boyle’s law

The woman in Figure 10 is taking a deep breath. This action helpsreduce her breathing rate and increase the volume of air she inhales.When you inhale, the volume of your chest cavity increases and airmoves into your lungs. When you exhale, the volume of your chestcavity decreases and air is pushed out of your lungs.

After you read this section, you will understand how changing thevolume of your chest cavity causes air to move into and out of yourlungs. Changes in the volume, the temperature, the pressure, and thenumber of particles have predictable effects on the behavior of a gas.

PressureAt many hockey rinks, a layer of shatterproof glass keeps the puck awayfrom the spectators. The force with which the puck hits the glassdepends on the speed of the puck. The faster the puck is traveling, thegreater the force is. The smaller the area of impact is, the greater thepressure produced. Pressure is the result of a force distributed over anarea. If the edge of the puck hits the glass, it exerts more pressure thanif the face of the puck hits the glass at the same speed.

The SI unit of pressure is derived from SI units for force and area.Force is measured in newtons (N) and area in square meters (m2).When a force in newtons is divided by an area in square meters, theunit of pressure is newtons per square meter (N/m2). The SI unit forpressure, the pascal (Pa), is shorthand for newtons per square meter.One pascal is a small amount of pressure. Scientists often expresslarger amounts of pressure in kilopascals. One kilopascal (kPa)is equal to 1000 pascals.

Figure 10 Taking a deep breathincreases the volume of yourchest cavity, which causes air tomove into your lungs.

isaffected

by

Gaspressure

a. ?

b. ?

c. ?

States of Matter 75

FOCUS

Objectives3.2.1 Define pressure and gas

pressure.3.2.2 Identify factors that affect

gas pressure.3.2.3 Predict changes in gas

pressure due to changes intemperature, volume, andnumber of particles.

3.2.4 Explain Charles’s law, Boyle’slaw, and the combined gas law.

3.2.5 Apply gas laws to solveproblems involving gases.

Build VocabularyParaphrase Replace less familiar wordsin a definition with more familiar wordsor phrases.

Reading Strategya. Temperature b. Volume c. Numberof particles

INSTRUCT

PressureBuild Science SkillsObserving

Purpose Show the effect of area on pressure.

Materials clay, CD case, textbook

Advance Prep Prepare two flattenedpieces of clay 3 cm thick.

Procedure Put the broad side of the CD case on a piece of clay with the bookon top. After about 30 seconds, carefullyremove the book and case. Then, put thecase on the other piece of clay, narrowside down. Balance the book on the casefor 30 seconds. (Place your hands oneither side of the book as a precaution.)Remove the book and case. Ask, How dothe depths of the imprints compare?(The imprint is deeper when the case isplaced on its edge.) What caused thisdifference? (Because the weight of thebook was applied to a smaller area, thepressure was greater.)

Expected Outcome When the sameforce is applied to a smaller area, thedepth of the imprint increases.Visual

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Reading Focus

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States of Matter 75

Print• Reading and Study Workbook With

Math Support, Section 3.2 and Math Skill: The Combined Gas Law

• Math Skills and Problem SolvingWorkbook, Section 3.2

•Transparencies, Section 3.2

Technology• Interactive Textbook, Section 3.2• Presentation Pro CD-ROM, Section 3.2• Go Online, Science News, Properties of matter

Section Resources

Section 3.2

PPLS

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76 Chapter 3

An object does not need to be as large as a hockey puck to exertpressure when it collides with another object. Recall that the heliumatoms in a balloon are constantly moving. The pressure produced bya single helium atom colliding with a wall is extremely small. However,there are more than 1022 helium atoms in a small balloon. When somany particles collide with the walls of a container at the same time,they produce a measurable pressure.

Collisions between particles of a gas and the walls of thecontainer cause the pressure in a closed container of gas. The morefrequent the collisions, the greater the pressure of the gas is. The speedof the particles and their mass also affect the pressure.

Factors That Affect Gas PressureThink again about the collisions that produce gas pressure. Whatchanges might affect the pressure of a gas in a container? The particlesin the gas could move faster or slower. The gas could be moved into alarger or smaller container. You could add gas or remove gas from thecontainer. Factors that affect the pressure of an enclosed gas areits temperature, its volume, and the number of its particles.

Temperature Suppose you are about to goon a long drive. The driver suspects that the airpressure in the automobile tires might be low.You check the pressure in each tire, using a pres-sure gauge like the one in Figure 11.You find thatthe measurements are well within the automo-bile manufacturer’s guidelines. If you checkedthe tire pressures again after a few hours on thehighway, would you be surprised to find that thepressure in the tires had increased?

The constant motion of tires on the highwaycauses the tires and the air in the tires to warmup. As the temperature rises, the average kineticenergy of the particles in the air increases. Withincreased kinetic energy, the particles move fasterand collide more often with the inner walls of the

tires. The faster-moving particles also hit the walls with greater force.The increase in the number of collisions along with the increase in theforce of the collisions causes an increase in the pressure of the air in thetires. Raising the temperature of a gas will increase its pressure ifthe volume of the gas and the number of particles are constant.

How does the frequency of collisions affect thepressure of a gas?

Figure 11 The fire-fighter is using apressure gauge tocheck the air pressurein a tire on a firetruck.If the tires on thetruck have a 44.5-inchdiameter, the pressureon a front tire shouldbe about 125 poundsper square inch (psi).

76 Chapter 3

Factors that AffectGas Pressure

Changing Volume of a Balloon

Purpose Students observe the effect oftemperature on the volume of a balloon.

Materials inflated balloons,refrigerator, warm place

Advance Prep One day ahead, inflatea balloon for each class. Place theballoons in a refrigerator overnight.

Procedure At the beginning of class,bring out a balloon and tell studentswhere it has been. Ask, Do you predictthat the volume of the balloon willincrease, decrease, or stay the sameafter the balloon has been in a warmplace? (Increase) Place the balloon in awarm place until shortly before the endof class. Make sure the balloon has roomto expand, and that the temperaturedoes not exceed 42°C. Ask, Whathappened to the volume of the gasinside the balloon? (It increased.)Explain that as temperature increases,the particles move faster, on average,which increases the pressure of the gasinside the balloon. The increasedpressure causes the balloon to expand.

Expected Outcome The balloon’svolume will increase as the temperatureincreases. Visual, Logical

Use Visuals Figure 11 Bring in a pressure gaugelike the one in the photo. (The gaugemeasures how much the air pressure inthe tire exceeds atmospheric pressure.)Have a volunteer note the units ofpressure on the gauge. (Pounds persquare inch) Explain that in the UnitedStates, pressure is not always measuredin SI units. Ask, Have you seen anyother units used for pressure?(Students may have seen barometricpressure reported in inches of mercury.)Why is data from experimentsmeasured and reported in SI units?(Scientists must use standard units so thattheir data can be shared with and testedby scientists in all countries.)Logical, Visual

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Section 3.2 (continued)

Customize for Inclusion Students

Visually Impaired Have students with visual impairments observedifferent air pressures in a bicycle tire. Bring abicycle tire and a pump with a built-in gauge.Let out all of the air in the tire. Attach the pumpto the inner tube valve. Read the pressure onthe gauge and allow students to feel that thetire is completely flat. Pump up the tire to a

third of the maximum recommended pressure(marked on the tire). Read the pressure on the gauge and allow students to feel the tireagain. Pump up the tire to the maximumrecommended pressure and allow students torepeat the observation. Discuss with studentshow the quantity of air in the tire affects thefirmness of the tire.

States of Matter 77

Volume Imagine that you have a plastic bottle that appears empty.If you twist the cap onto the bottle and then squeeze the bottle, whatwill happen? At first, the plastic will give a little, reducing the volumeof the bottle. But soon you will feel pressure from inside the bottleresisting your efforts to further reduce the volume. The pressure youfeel is a result of the increased pressure of the air trapped inside thebottle. As the volume is decreased, particles of trapped air collide moreoften with the walls of the bottle. Reducing the volume of a gasincreases its pressure if the temperature of the gas and the numberof particles are constant.

Figure 12 shows how the relationship between volume and pres-sure explains what happens when you breathe. As you inhale, a musclecalled the diaphragm (DY uh fram) contracts. The contraction causesyour chest cavity to expand. This temporary increase in volume allowsthe particles in air to spread out, which lowers the pressure inside thechest cavity. Because the pressure of the air outside your body is nowgreater than the pressure inside your chest, air rushes into your lungs.

When you exhale, your diaphragm relaxes and the volume of yourchest cavity decreases. The particles in the air are squeezed into asmaller volume and the pressure inside your lungs increases. Becausethe pressure of the air inside your chest is now greater than the pres-sure of the air outside your body, air is forced out of your lungs.

Number of Particles You can probably predict what willhappen to the pressure when you add more gas to a container. Thinkabout a tire. Once the tire is inflated, its volume is fairly constant. Soadding more air will increase the pressure inside the tire. The moreparticles there are in the same volume, the greater the number of col-lisions and the greater the pressure. At some point the rubber fromwhich the tire is made will not be strong enough to withstand theincreased pressure and the tire will burst. Increasing the numberof particles will increase the pressure of a gas if the temperature andthe volume are constant.

Lungs

Inhaling Exhaling

Rib cage

Diaphragm

Diaphragm contracts.Rib cage is lifted

up and out.

Diaphragm relaxes.Rib cage movesdown and in.

Figure 12 Movement of amuscle called the diaphragmchanges the volume of your chestcavity. The volume increaseswhen you inhale and decreaseswhen you exhale. Interpreting Diagrams Howdoes the movement of your ribcage affect the volume of yourchest cavity?

For: Articles on properties ofmatter

Visit: PHSchool.com

Web Code: cce-1032

Build Reading LiteracyPredict Refer to page 66D in thischapter, which provides the guidelinesfor predicting.

List on the board examples of volume,temperature, and number of particlesincreasing or decreasing. Tell students to predict how each change will affectgas pressure in a closed container. Askstudents to use the number of particlecollisions to explain their predictions. As students provide their predictionsand explanations, write the correcteffect on pressure and the correctexplanation on the board. Logical, Portfolio

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States of Matter 77

Science News provides studentswith current information onproperties of matter.

Answer to . . .

Figure 12 The volume increases asthe rib cage is lifted up and out. Thevolume decreases as the rib cagemoves down and in.

The more frequent thecollisions, the greater

the pressure of the gas is.

Fainting Couches During the Victorian era,well-to-do households often had faintingcouches. The tightly laced, whalebone corsetswomen wore restricted their ability to breathedeeply. As a result, they had low levels of oxygen

in their blood, causing them to faint, or swoon.Today, Victorian fainting couches can be seen in historic houses or museums. Antique faintingcouches and reproductions are available in somefurniture and antique stores.

Facts and Figures

0066_hsps09te_Ch03.qxp 4/18/07 10:39 AM Page 77

78 Chapter 3

Charles’s LawDuring his lifetime, the French physicist Jacques Charles (1746–1823)was known for his inventions, including the hydrogen balloon. Today,Charles is best known for his investigations of the behavior of gases.Charles collected data on the relationship between the temperatureand volume of gases. When he graphed the data, the graph was astraight line, as shown in Figure 13. The graph shows that the volumeof a gas increases at the same rate as the temperature of the gas.

Charles extended the line on his graph beyond the measured datato see what the temperature would have to be to produce a volume of0 L. The temperature at the point where the line crossed the x-axis was�273.15°C. This temperature is equal to 0 K on the Kelvin tempera-ture scale. A temperature of 0 K is called absolute zero. No scientist hasproduced a temperature of absolute zero in a laboratory, but some havecome extremely close. As a gas cools to temperatures near 0 K, the gaschanges to a liquid, a solid, or sometimes a Bose-Einstein condensate.

Charles’s law states that the volume of a gas is directly propor-tional to its temperature in kelvins if the pressure and the number ofparticles of the gas are constant. Charles’s law can be written as amathematical expression in which T1 and V1 represent the tempera-ture and volume of a gas before a change occurs. T2 and V2 representthe temperature and volume after a change occurs.

Charles’s Law

�

The temperatures must be expressed in kelvins. If temperatures indegrees Celsius are used in the expression, the volume will not bedirectly proportional to the temperature.

V2T2

V1T1

Figure 13 These graphs comparethe effects of temperature andvolume on the pressure of a gas.Charles’s law describes the directrelationship between thetemperature and the volume.Boyle’s law describes the inverserelationship between the volumeand the pressure. Controlling Variables For eachgraph, name the manipulatedvariable and the respondingvariable.

Volume (L)

Pres

sure

(kP

a)

250

200

150

100

50

00 0.5 1.0 1.5 2.0 2.5

Boyle’s LawCharles’s Law

Temperature (�C)

Vo

lum

e (m

L)

10

8

6

4

2

0�300 �250 �200 �150 �100 �50 0 50 100

�273.15

78 Chapter 3

Charles’s Law Build Science SkillsUsing Tables and Graphs Havestudents analyze Figure 13. Havestudents look first at the graph forCharles’s law. Point out the straight line with the positive slope. Ask, Whatrelationship does this line describe? (It describes a direct relationship betweenvolume and temperature: As temperatureincreases, volume also increases.) Ask,Why is part of the line solid and partdashed? (The solid line represents actualdata, while the dotted line is the extensionof the collected data toward the zero pointfor volume.) Have students refer to theBoyle’s Law graph. Ask, What happensto pressure as volume increases? (Asvolume increases, pressure decreases.)Visual, Logical

Build Math SkillsLine Graphs Students are likely to need help understanding why Charles’slaw does not apply when temperaturesare expressed in degrees Celsius. Havestudents find the point on the graphwhere the temperature is 0ºC and askthem to estimate the volume at thattemperature. Then, tell them that thestraight line must pass through (0, 0) forthe responding variable to be directlyproportional to the manipulated variable.Logical, Portfolio

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text foradditional help.

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Section 3.2 (continued)

Absolute Zero Based on the decrease in the volume of a gas as it cooled, scientistshypothesized that if an ideal gas were cooledto absolute zero (0 K on the Kelvin temperaturescale or �273.15 on the Celsius scale), itsvolume would be zero. However, as actualgases are cooled, they reach temperatures atwhich they change to liquids or solids.

Theoretically, all motion of particles in mattershould cease at absolute zero. But according to quantum mechanics, a substance will containsome energy of motion, regardless of its temper-ature. For that reason, substances cannot becooled to absolute zero. However, Bose-Einsteincondensates produced in laboratories exist attemperatures very close to absolute zero.

Facts and Figures

States of Matter 79

Materialspan, metric ruler, empty beverage can, maskingtape, hot plate, clock, tongs

Procedure1. Fill a pan with cold water to a depth of 3 cm.

2. Use masking tape to cover half the openingof the can. CAUTION Do not cover the entireopening with tape.

3. Place the can on the hot plate and turn thehot plate to a high setting. Heat the can for5 minutes and then turn off the hot plate.

4. Use tongs to remove the can from the hot plateand place it upside down in the pan of water asshown. The opening should be below thesurface of the water. Observe the can as it cools.

Analyze and Conclude1. Inferring How did the temperature of the air

inside the can change when you heated thecan? How did it change when you put the canin the water?

2. Drawing Conclusions What happened tothe pressure of the air inside the can whenyou put the can in the cold water?

3. Inferring Did the air pressure outside thecan change during the experiment?

4. Formulating Hypotheses What caused thechange you observed in Step 4?

Observing the Effect ofTemperature on Gas Pressure

Boyle’s Law Robert Boyle, who was born in Ireland in 1627, was the first to describethe relationship between the pressure and volume of a gas. The graph inFigure 13 shows what happens when the volume of a cylinder contain-ing a set amount of gas is decreased. What happens when the volume ofthe cylinder is reduced from 2.0 liters to 1.0 liter? The pressure of thegas in the cylinder doubles from 50 kilopascals to 100 kilopascals.

Boyle’s LawP1V1 � P2V2

Boyle’s law states that the volume of a gas is inversely proportionalto its pressure if the temperature and the number of particles are con-stant. Boyle’s law can be expressed mathematically. P1 and V1 representthe pressure and volume of a gas before a change occurs. P2 and V2represent the pressure and volume of a gas after a change occurs.

How is Boyle’s law expressed mathematically?

Boyle’s Law

Observing the Effect of Temperature on Gas Pressure

ObjectiveAfter completing this activity, studentswill be able to• predict the effect of temperature on

the pressure of a gas.

This lab helps dispel the misconceptionthat a gas does not have mass. Explainthat air pressure is the result of particlesin air colliding with the can. The force of the collisions (and pressure) dependson the mass and speed of the particles.

Skills Focus Inferring

Prep Time 10 minutes

Materials pan, metric ruler, emptybeverage can, masking tape, hot plate,clock, tongs

Advance Prep Ask students tocontribute clean, empty beverage cans.Use dissecting pans, cake pans, orplastic dishpans.

Class Time 20 minutes

Safety Caution students not to touchthe hot plate or the can once the hotplate has been turned on.

Expected Outcome The can will crackor collapse within one minute afterbeing placed in cold water.

Analyze and Conclude1. The temperature increased when thecan was heated and decreased when itwas placed in cold water.2. The pressure decreased.3. The air pressure outside the can didnot change.4. As the gas inside the can cooled, itspressure decreased until it could nolonger offset the outside air pressure.

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States of Matter 79

Answer to . . .

Figure 13 For Charles’s law, themanipulated variable is temperatureand the responding variable is volume.For Boyle’s law, the manipulatedvariable is volume and the respondingvariable is pressure.

P1V1 � P2V2

Experimental Evidence Robert Boyle was a founding member of The Royal Society,the oldest continuous scientific society in the world. The society’s motto is Nullius inVerba, Latin for “Nothing in Words.” Themotto means that science should be based on experimental evidence, not debates.

Boyle’s adherence to a scientific methodwas one of his most important contributionsto science. He was among the first scientists

to publish detailed experimental results, evenresults of unsuccessful experiments. In 1661,Boyle’s The Sceptical Chymist was published. It disputed Aristotle’s theories about elements.His 1662 publication of The Spring and Weightof the Air included experiments that led toBoyle’s law. For these and earlier experiments,Boyle developed an improved vacuum pump,which required only one person to operate.

Facts and Figures

The Combined Gas LawThe relationships described by Boyle’s law and Charles’s law can bedescribed by a single law. The combined gas law describes the rela-tionship among the temperature, volume, and pressure of a gas whenthe number of particles is constant.

Combined Gas Law

�

The combined gas law is used to solve many problems involving gases.

P2V2T2

P1V1T1

80 Chapter 3

The Combined Gas LawA cylinder that contains air at a pressure of 100 kPa has a volumeof 0.75 L. The pressure is increased to 300 kPa. The temperaturedoes not change. Find the new volume of air.

Read and UnderstandWhat information are you given?

P1 � 100 kPa P2 � 300 kPa V1 � 0.75 L

Plan and SolveWhat unknown are you trying to calculate?

V2

What expression can you use?

�

Cancel out the variable that does not change and rearrangethe expression to solve for V2.

P1V1 � P2V2 V2 �

Replace each variable with its known value.

V2 � 100 kPa � � 0.25 L

Look Back and CheckIs your answer reasonable?

Volume should decrease as pressure increases. Thepressure tripled from 100 kPa to 300 kPa. The answer,0.25 L, is one third the original volume, 0.75 L.

0.75 L300 kPa

P1V1P2

P2V2T2

P1V1T1

1. A gas has a volume of 5.0 L at apressure of 50 kPa. What happensto the volume when the pressureis increased to 125 kPa? Thetemperature does not change.

2. Gas stored in a tank at 273 K hasa pressure of 388 kPa. The safelimit for the pressure is 825 kPa.At what temperature will the gasreach this pressure?

3. At 10ºC, the gas in a cylinder hasa volume of 0.250 L. The gas isallowed to expand to 0.285 L.What must the final temperaturebe for the pressure to remainconstant? (Hint: Convert fromdegrees Celsius to kelvins usingthe expression ºC � 273 � K.)

Build Math SkillsFormulas and Equations A gas has apressure of 200 kPa in a 0.5-L container.Use Boyle’s law to determine the pressureof the gas in a 2.0 container. (50 kPa)Logical

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text foradditional help.

The Combined Gas LawIntegrate MathHave students show how the combinedgas law can be used to derive Boyle’s andCharles’s laws. If temperature is constant,the temperature cancels out to revealBoyle’s law P1V1 � P2V2. Similarly, ifvolume remains constant, Charles’s lawof P1/T1 � P2/V2 is derived. Logical

Solutions1. V2 � (P1V1/P2) �(50 kPa)(5.0 L)/125 kPa � 2.0 L2. T2 � (P2T1/P1) �(825 kPa)(273 K)/388 kPa � 580 K3.T2 � (V2T1/V1) �(0.285 L)(283 K)/0.250 L �323 K or 50°C Logical

For Extra Help Remind students that before they solve aspecific problem, they should determinewhich variable is not changing andremove that variable from the combinedgas law. Then, they need to identifywhich of the variables is the unknown—V2, T2, or P2—and rearrange the equa-tion to solve for that variable. If studentsare having trouble rearranging theequation, provide students with the sixpossible forms of the equation. Logical

Additional Problems1. A gas is stored at constant volume ata pressure of 137 kPa at 274 K. If thetemperature rises to 296 K, what is thepressure? (148 kPa)2. At constant temperature, the volumeof a gas at 1000 kPa is changed from100 L to 10 L. What is the new pressure?(10,000 kPa) Logical

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Section 3.2 (continued)

Weather Balloons Large weather balloonsare made of natural or synthetic rubber. Theyare filled with either helium or hydrogen. Asthe balloon expands, the thickness of therubber decreases from about 0.051 mm to0.0025 mm at the altitude when the balloonbursts. A balloon that is about 2 m in diameterat launch will be about 6 m in diameter after itexpands. Balloons are launched twice a day atsites around the world.

Attached to the weather balloon is aradiosonde, an instrument that measurespressure, temperature, and relative humidity.Because the radiosonde can be reconditionedand used again, a parachute and mailing bagare also attached to the weather balloon. (Thephotograph in Figure 14 was taken at theNational Weather Station in Maryland.)

Facts and Figures

80 Chapter 3

Section 3.2 Assessment

Reviewing Concepts1. How is the gas pressure produced in a

closed container of gas?

2. What three factors affect gas pressure?

3. How does increasing the temperatureaffect the pressure of a contained gas?

4. What happens to the pressure of a gas ifits volume is reduced?

5. How does increasing the number ofparticles of a contained gas affect its pressure?

Critical Thinking 6. Predicting What happens to the pressure

in a tire if air is slowly leaking out of the tire?Explain your answer.

7. Comparing and Contrasting What doBoyle’s law and Charles’s law have incommon? How are they different?

8. Applying Concepts Some liquid productsare sold in aerosol cans. Gas is stored in a canunder pressure and is used to propel the liquidout of the can. Explain why an aerosol canshould never be thrown into a fireplaceor incinerator.

9. Two liters of hydrogen gas are stored at apressure of 100 kPa. If the temperaturedoes not change, what will the volumeof the gas be when the pressure isdecreased to 25 kPa?

10. You know that a gas in a sealed containerhas a pressure of 111 kPa at 23ºC. Whatwill the pressure be if the temperature risesto 475ºC?

It is harder for scientists to do a controlled experimentwhen they are studying events that occur in natural settings.Scientists need laws like the combined gas law to deal with sit-uations in which multiple variables are changing. Balloons likethe one in Figure 14 are used by scientists to gather data aboutEarth’s atmosphere. The balloon is filled with hydrogen orhelium. It carries a package of weather instruments up intothe atmosphere. The instruments measure temperature, pres-sure, and water content at different levels in the atmosphere.

What will happen to the volume of the weather balloon asit rises through the atmosphere? Both pressure and temperaturedecrease as the altitude increases in Earth’s atmosphere. Adecrease in external pressure should cause the balloon to expandto a larger volume. A decrease in temperature should cause theballoon to contract to a smaller volume. Whether the balloonactually expands or contracts depends on the size of the changesin pressure and temperature.

States of Matter 81

Figure 14 These scientists are releasing aweather balloon into the atmosphere. Theballoon is designed to burst when it reachesan altitude of about 27,400 meters. Drawing Conclusions What happens to thepressure inside a weather balloon as it rises?

Use VisualsFigure 14 The balloon will burst when it reaches an altitude of about 27,400 m.Ask, What variables change as theballoon rises? How do they change?(Temperature and pressure both decrease.)How does each change affect thevolume of the balloon? (Decreasingatmospheric pressure causes the balloon to expand. Decreasing temperature causesthe balloon to shrink.)Visual, Logical

ASSESSEvaluate UnderstandingHave students look at the mathematicalpresentations of Charles’s law on p. 78and Boyle’s law on p. 79 and describethe relationships in their own words.

ReteachWrite Charles’s law and Boyle’s law on the board. Have students quiz each other about the behavior of theresponding variable when anothervariable increases or decreases.

Solutions9. V2 � (P1V1/P2) �(100 kPa)(2.0 L)/25 kPa � 8.0 L10. P2 � (P1T2/T1) �(111 kPa)(748 K)/296 K � 280 kPa

If your class subscribesto the Interactive Textbook, use it toreview key concepts in Section 3.2.

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L2

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States of Matter 81

Answer to . . .

Figure 14 The pressure increases.

4. If the volume is reduced, the pressure of agas increases if temperature and number ofparticles are constant. 5. Increasing the number of particles willincrease the pressure if temperature andvolume are constant.6. Because the number of particles of air isreduced from the leak, the pressure willslowly decrease.

7. Both laws describe a relationship betweentwo variables that affect a gas when othervariables are constant. Charles’s law showshow the volume of a gas is directly propor-tional to its temperature in kelvins. Boyle’slaw shows how the volume of a gas isinversely proportional to its pressure. 8. At a high temperature, the pressure in thegas might increase to the point where thecan would explode.

Section 3.2 Assessment

1. Collisions between particles of a gas andthe walls of the container cause the pressurein a closed container of gas.2. Temperature, volume, and number of particles3. Raising the temperature will increase thepressure if volume and number of particlesare constant.

Riding on AirWarm air is less dense than cold air. So if enough warm air isconfined to a lightweight container, the container can risethrough the surrounding colder air. This is the principle thatallows a hot-air balloon to get off and stay off the ground.

Taking Off and LandingLaunching and piloting a hot-airballoon is an activity that takes skilland patience.

■1 The crew uses fansto fill the envelopewith cold air.

■3 Once up, the pilotmaintains altitude by

occasionally turningon the burner for a

few seconds.

■4 To lose altitude, thepilot opens a valve at

the top of the envelopeto let out some hot air.

Valve

Burner

■2 Gas burners are switchedon to heat the air and

inflate the balloon, which begins to rise.

When air is heated, the particles in the airgain energy and move faster on average. Theparticles also move farther apart, so a givenvolume of hot air contains fewer particlesand has less mass than the same volume ofcold air. This difference in density producesan upward force. In a hot-air balloon, theforce is very small, equivalent to lifting aboutone tenth of a gram for each liter of air. Alarge volume of air is needed to support themass of the balloon and any passengers. Thatis why hot-air balloons need to be large.

To heat the air, the pilot burns propanegas, which is stored under pressure in tanks.The bottom of the balloon’s envelope (theskirt) is treated so that it is not flammable.

As the balloon nears thechosen altitude, the pilot turns theburner off so that the balloon willstop rising. The pilot maintains thealtitude of the balloon by turning theburner on and off and by opening a valveat the top of the balloon to let hot air escape.

The horizontal movement of the balloon ismuch harder to control. The wind speed andwind direction vary at different altitudes. Thepilot uses the burner and the valve to changethe altitude of the balloon and take advantageof favorable winds. A hot-air balloon cannotland at the same spot from which it took off.The ground crew must drive to the landing siteto collect the balloon and the passengers.

82 Chapter 3

82 Chapter 3

Riding on AirBackgroundOn August 27, 1783, Jacques Charlesreleased his first hydrogen-filled balloon,which was about 4 m in diameter. Heprepared the hydrogen by pouringsulfuric acid over scrap iron. Charles alsomade improvements to hot-air balloons,including a valve line that allowed oper-ators to release gas from the balloonand a wicker basket (a nacelle), whichwas attached to the balloon by ropes.The first publication of Charles’s workwas by Joseph Gay-Lussac, who referredto Charles’s work in an 1802 paper. Gay-Lussac also did ballooning. Hisaltitude record of 7016 m (4.3 miles)stood for almost 50 years.

Build Science SkillsObserving

Purpose Students will observe that heating air causes it to expand and become less dense.

Materials plastic bag (dry cleaner orthin garbage bag), string, hair dryers

Class Time 20 minutes

Procedure Organize students intogroups of two or three. Have studentstie a string around the closed end of theplastic bag and place evenly spacedpaper clips around the open end asweights. Tell students to hold the openend of the plastic bag over the hairdryer (set on high) and let the bag fillwith hot air. The plastic bag begins torise as it fills with hot air. When thestudents feel the bag begin to rise, havethem release the bag. Ask, What causesthe bag to rise? (The heated air insidethe bag is less dense than the air outsidethe bag.) Use what happened to theplastic bag to explain how a hot-airballoon works. (A hot-air balloon risesbecause air in the balloon is heated.)

Expected Outcome When the airinside the bag is heated, the bag begins to rise.Visual, Group

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L2

� Write a paragraph comparing early hot-airballoons with modern balloons. Include thefollowing information: thekind of materials used, thelength of distances traveled,and the types of fuel used.

� Take a Discovery Channel Video Field Trip by watching“Up, Up, and Away.”

Going Further

■5 The pilot selects asuitable place to landbefore opening thevalve all the way.

■6 The balloon slowlyfalls to the groundand collapses.

■7 The crewgathers up theenvelope.

Balloon ValveThe valve helps to control the balloon’s altitude.When the valve is opened, some hot air isreleased from the top of the balloon. The hot airis replaced by cold air flowing into the base ofthe balloon. This exchange of cold air for hot airincreases the mass of the balloon, causing it todescend until the pilot closes the valve.

Jet of flamefrom burner

Envelopemade from

tough nylon

Flexible, lightweight,wicker basket

Flame-resistant skirt

Particle PressureParticles in hot air move fasterand are farther apart than thosein cold air, so hot air is less densethan cold air. With lower density,heated air rises over colder air.

Slower-movingcold airparticles

Fast-movinghot airparticles

Upwardforce

States of Matter 83

Video Field Trip

Going FurtherThe Montgolfier hot-air balloon that first carried human passengers had anenvelope made of cotton and papercoated with alum to reduce flammability.The fuel used was straw. The balloon flewfrom the center of Paris to the outskirts (a distance of about 9 kilometers) in 25 minutes on November 21, 1783.(Hot-air balloons were soon eclipsed byhelium balloons or hydrogen balloons.)Modern passenger hot-air balloons weredeveloped in the United States in the1960s. Their envelopes are made ofnylon and they use propane fuel. Hot-airballoons generally stay aloft for about an hour. (For long distance flights,balloonists generally use combinationhelium and hot-air balloons called Rozier balloons after Pilâtre de Rozier, apassenger on the first “manned” flight.)Verbal

States of Matter 83

After students have viewed the Video FieldTrip, ask them the following questions: Whatgases have commonly been used in balloonsthat carry passengers? (Hot air, helium, andhydrogen) Why do the particles of a gasinside a balloon fill the entire balloon?(A gas has no particular size or shape andexpands to fill the volume available.) What

causes a hot-air balloon to lift off and risefrom a surface? (Hot air inside the balloon isless dense than the cooler, denser air outside theballoon. The difference in density results in anupward force.) In 1931, Auguste Piccard, aSwiss physicist and educator, built a balloonthat could rise a distance of 16 miles. Why did Piccard design the balloon so that itcould become airborne when it was onlypartially filled? (Piccard knew the gas inside the balloon would continue to expand as theballoon floated up to greater heights because

the outside air pressure decreased as the balloonrose.) In Piccard’s balloon, the pressure in thecabin was controlled as it is in planes thattravel at great heights above Earth’s surface.Air pressure in the cabin is kept higher thanatmospheric pressure. Why must the airpressure inside the cabin be controlled?(Atmospheric pressure decreases with altitudeuntil it no longer can sustain respiration.)

Video Field Trip

Up, Up, and Away

0066_hsps09te_Ch03.qxp 4/18/07 10:40 AM Page 83

3.3 Phase Changes

Reading Strategy Summarizing Copy the diagram. As youread, complete the description of energy flowduring phase changes.

Key ConceptsWhat are six commonphase changes?

What happens to asubstance’s temperatureand a system’s energyduring a phase change?

How does thearrangement of watermolecules change duringmelting and freezing?

How are evaporation andboiling different?

Vocabulary◆ phase change◆ endothermic◆ heat of fusion◆ exothermic◆ vaporization◆ heat of vaporization◆ evaporation◆ vapor pressure◆ condensation◆ sublimation◆ deposition

Massive chunks of frozen water called icebergs are a common sightoff the continent of Antarctica. A large iceberg like the one in Figure 15contains enough fresh water to supply millions of people with waterfor a year. During the summer in southern Australia, fresh water is ascarce resource. People have proposed towing icebergs to Australiafrom Antarctica. The plan has not been implemented because the tripcould take months to complete and much of the iceberg would meltalong the way. In this section, you will find out what happens when asubstance, such as water, changes from one state to another.

Characteristics of Phase ChangesWhen at least two states of the same substance are present, scientistsdescribe each different state as a phase. For example, if an iceberg is float-ing in the ocean, there are two phases of water present—a solid phaseand a liquid phase. A phase change is the reversible physical change thatoccurs when a substance changes from one state of matter to another.

Endothermic Exothermic

LiquidSolid a. ? Solid

b. ? c. ? d. ?

Solid e. ? f. ?

Gas

Solid

84 Chapter 3

Figure 15 The solid and liquidphases of water are visible in thisphotograph of an iceberg in theAmundsen Sea near Antarctica.

84 Chapter 3

FOCUS

Objectives3.3.1 Describe phase changes.3.3.2 Explain how temperature can

be used to recognize a phasechange.

3.3.3 Explain what happens to themotion, arrangement, andaverage kinetic energy of watermolecules during phasechanges.

3.3.4 Describe each of the six phasechanges.

3.3.5 Identify phase changes asendothermic or exothermic.

Build VocabularyWord-Part Analysis List on the boardthe following word parts and meanings:-ion, “the act of” or “the result of anaction”; -ic, “related to or characterizedby”; endo-, “inside”; exo-, “outside”;therm, “heat”; -ize, “to become.” Havestudents identify these word parts in thevocabulary terms. Discuss the terms’meanings with students.

Reading Strategya. Liquid b. Liquid c. Gas d. Liquide. Gas f. Gas

INSTRUCT

Characteristics ofPhase ChangesUse VisualsFigure 15 Note that water is one ofthe few substances that exist naturally as a solid, liquid, and gas under ordinaryconditions. Have students look at thefigure and read the caption. Ask, Whichtwo phases of water are visible in thephotograph? (Solid and liquid) Wherewould the third phase most likely befound? (In the air)Visual, Logical

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Reading Focus

1

Section 3.3

Print• Laboratory Manual, Investigation 3A • Reading and Study Workbook With

Math Support, Section 3.3Transparencies, Section 3.3

Technology• Probeware Lab Manual, Lab 1 • Interactive Textbook, Section 3.3• Presentation Pro CD-ROM, Section 3.3• Go Online, NSTA SciLinks, Phases of matter;

PHSchool.com, Data sharing

Section Resources

States of Matter 85

In Figure 16, a state of matter is listed at each corner of the triangle.Each arrow in the diagram represents a different phase change. Eachpair of arrows represents a set of reversible changes. For example, thearrow starting at the solid phase and ending at the liquid phase repre-sents melting. The arrow starting at the liquid phase and ending at thesolid phase represents freezing.

Melting, freezing, vaporization, condensation, sublimation,and deposition are six common phase changes. All phase changesshare certain characteristics related to energy and temperature.

Temperature and Phase Changes One way torecognize a phase change is by measuring the temperature ofa substance as it is heated or cooled. The temperature ofa substance does not change during a phase change.

Naphthalene (NAF thuh leen) is a compound that is sometimes usedin mothballs. Figure 17 is a graph of the data collected when a solidpiece of naphthalene is slowly heated. Temperature readings are takenat regular intervals. At first the temperature rises as the solid naphtha-lene warms up. But at 80°C, the temperature of the naphthalene stopsrising. The temperature remains at 80°C, which is the melting point ofnaphthalene, until melting is complete.

If liquid naphthalene is placed in an ice-water bath, the temperatureof the liquid will drop until it reaches 80°C. It will remain at 80°C untilall the liquid freezes. The temperature at which the substance freezes—its freezing point—is identical to the temperature at which it melts. Thefreezing and melting points of naphthalene are both 80°C.

If naphthalene is heated after it has completely melted, its tempera-ture begins to rise again. The temperature keeps rising until it reaches218°C, which is the boiling point of naphthalene. Until boiling is com-plete, the temperature remains at 218°C.

Time (minutes)

Tem

per

atu

re (

�C)

100

90

80

70

60

50

40

30

200 1 2 3 4 5 6 7 8

Heating Curve for Naphthalene

Figure 17 This graph shows whathappens to the temperature of asolid sample of naphthalene asthe sample is slowly heated. Using Graphs What happenedto the temperature in the intervalbetween four and seven minutes?

Figure 16 This diagram lists sixphysical changes that can occuramong the solid, liquid, andgaseous phases of a substance.Interpreting Diagrams Explainwhy the changes are grouped intothe pairs shown on the diagram.

Melting

Freezing

Condensation

VaporizationSubl

imat

ion

Dep

ositi

on

Solid Liquid

Gas

For: Links on phase diagrams

Visit: www.SciLinks.org

Web Code: ccn-1030

Build Reading LiteracyRelate Text and Visuals Refer topage 190D in Chapter 7, whichprovides the guidelines for relating text and visuals.

As students read the section, have themrefer to Figure 17. Ask, In what state isthe naphthalene at 20°C? In what stateis the naphthalene at 90°C? (Solid, liquid)What are the melting and freezingpoints of naphthalene? (Both are 80°C.)What would the heating curve fornaphthalene look like if the graph were extended beyond a temperatureof 100°C? (The heating curve would riseuntil it reached the boiling point ofnaphthalene, which is 218°C.)Visual, Logical

FYIThe plateau on the graph in Figure 17 isnot completely flat as it should be whilea substance melts. This graph representsactual data collected in a lab. It is likelythat there were some impurities in thenaphthalene sample, which caused someminor fluctuation in the melting point.

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States of Matter 85

Customize for English Language Learners

Build a Science GlossaryDirect students to Figure 16. Before they read,have them use the figure to make a list of thesix terms in the arrows for a glossary. Students

should add definitions for the terms to theglossary as they read the section. Encouragestudents to include examples of the six phasechanges along with the definitions.

Answer to . . .

Figure 16 The groupings representpairs of reversible changes.

Figure 17 The temperature remainedfairly constant.

PPLS

Download a worksheet on phasediagrams for students to complete,and find additional teacher supportfrom NSTA SciLinks.

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Energy absorbed

86 Chapter 3

Energy and Phase Changes During a phase change, energyis transferred between a substance and its surroundings. The directionof the transfer depends on the type of phase change. Energy iseither absorbed or released during a phase change.

The ice sculpture in Figure 18 isn’t going to last forever. When thetemperature of the air rises above 0°C or when sunlight shines directlyon the ice, an ice sculpture begins to melt. Melting is an example of anendothermic change. During an endothermic change, the systemabsorbs energy from its surroundings.

The amount of energy absorbed depends on the substance. Forexample, one gram of ice absorbs 334 joules (J) of energy as it melts.This amount of energy is the heat of fusion for water. Fusion is anotherterm for melting. The heat of fusion varies from substance to substance.

One gram of water releases 334 joules of energy to its surroundingsas it freezes, the same amount of energy that is absorbed when one gramof ice melts. Farmers use this release of energy to protect their crops.When farmers expect temperatures to drop slightly below 0°C, theyspray the crops with water as shown in Figure 19. As water freezes, itreleases heat. The flow of heat slows the drop in temperature and helpsprotect the crops from damage. Freezing is an example of an exother-mic change. During an exothermic change, the system releases energyto its surroundings.

An understanding of phase changes can be useful in many situa-tions. The How It Works box explains how the design of an ice rink inUtah allows the manager of the rink to control the hardness of the ice.

How much energy does one gram of ice absorb asit melts?

Figure 18 This ice sculpture of adog sled was carved at a winterfair in Fairbanks, Alaska. The icesculpture will start to melt if thetemperature rises above 0ºC orsunlight shines directly on the ice.

Figure 19 Energy released as iceforms on these strawberry plantskeeps the plants from freezing attemperatures slightly below 0°C.Applying Concepts Explainwhy a farmer would need tokeep spraying the plants withwater while the temperatureremains below freezing.

Energy released

86 Chapter 3

Integrate BiologyOne of the main causes of frost damagein crops is ice-nucleating bacteria. Thesebacteria provide a nucleus around whichice can form. When ice forms on plants, itpierces their cell walls and causes the cellsto desiccate, or dry out because waterescapes from the cells. Have studentssearch the Internet for information onice-nucleating bacteria. Have studentspresent what they learn in a pamphletthat offers suggestions on how to preventfrost damage from bacteria. Verbal

Energy Transfer

Purpose Students observe that thephase change from ice to water isendothermic.

Materials tray of ice cubes

Procedure Place a tray of ice cubes on a counter at the beginning of class. As theice begins to melt, ask students where theenergy to melt the ice comes from.

Expected Outcome Students willobserve that the ice melts. They will inferthat the energy to melt the ice comesfrom the air and the counter becausethese materials are warmer than the ice.Visual

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Section 3.3 (continued)

Preventing Frost Damage For a frostcontrol system to work, a farmer needs to startthe sprinklers just before the temperature atground level reaches 0°C. Placing a shallowpan of water in the lowest part of the field is aneasy way to monitor the temperature. As soonas ice begins to form around the edge of thepan, the sprinklers should be turned on. Thesprinklers should stay on until the temperaturerises enough to start melting the ice.

This method of frost control is effective for strawberry plants down to about �6.6°C.When strawberries are in bloom, sprinklers are best started at 1.1°C. Blueberries withopen blooms are safe from damage at tem-peratures as low as 0°C. Because of the cost of installation and operation, frost controlsystems are generally used for crops that candemand high unit prices, such as oranges,strawberries, Blueberries, and asparagus.

Facts and Figures

States of Matter 87

Custom-Tailored Ice At the Utah Olympic Oval the hardness of the ice can becontrolled. The ice must be cold and hard for long speed-skating races, where the length of a skater’s glide isimportant. For shorter races, the skaters need moretraction, so the ice is made a little warmer and softer.Interpreting Diagrams What is the purpose of thesand layer?

Speed SkaterThis skater is racing at the UtahOlympic Oval, one of theworld’s most technicallyadvanced ice rinks.

Sand layer To preventthe gravel layer from

freezing, which coulddamage the rink structure,the sand layer is kept at atemperature above 0°C.

Gravel layer This layerprovides the foundation

for the rink.

Chilled concrete slab Thetemperature is controlled by cold

salt water, which is pumped throughpipes embedded in the slab. The saltwater remains liquid because its freezingpoint is lower than that of pure water.

Paint layer withmarkings

Paint layer with logos

Paint layer withbackground color

Ice layersThe skating surface is formed with asmany as 24 layers of ice and paint. Warm water is used for the top layers because it contains less dissolved air, and canproduce a denser, harder, frozen surface.

Skating surface The surface is built up fromthin layers of ice to a depth of less than 2 cm.

The ice can be as cold as –8°C. The temperature andthe hardness of the ice are controlled by tiny changesto the temperature of the underlying concrete layer.

Lubricant

Insulating layers These layersprevent heat from rising up

into the concrete slab from thewarmer sand layer underneath.

Custom-Tailored IceSkaters traveling at speeds up to80 km/h will be slowed by a surface thatis not smooth, level, and uniformly hard.The conditions of the ice at the UtahOlympic Oval, which was constructedfor the 2000 Winter Olympics, can bechanged overnight. For sprinters, the iceis softer so that their traction, or abilityto grip the ice, is greater. A hardersurface allows long-distance skaters to glide more easily across the ice.

Controlling the indoor climate is also important in maintaining the icesurface. The Utah Olympic Oval has twoair-filtering systems and a dehumidifierthat can reduce humidity to 3%. The airtemperature varies only 3°C from the iceto the ceiling. Controlling the conditionsabove and below the ice allows forprecise control of the ice surface.

Interpreting Diagrams The sandlayer prevents the gravel layer fromfreezing and damaging the rinkstructure. Visual, Logical

For EnrichmentHave students research playing surfacesused in other sports, such as football,tennis, and golf. Explain that differentsurfaces affect an athlete’s performance.Students could compare the advantagesand disadvantages of artificial turf andgrass football fields; or cement, clay, andgrass tennis courts. They could also findout how the length of grass affects shotsat different locations on a golf course.Logical

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States of Matter 87

Answer to . . .

Figure 19 Until the temperature risesabove freezing, the farmer mustcontinue to provide energy to keep theplants from freezing.

334 joules

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88 Chapter 3

Melting and FreezingIn water, hydrogen and oxygen atoms are combined in small unitscalled molecules. Each water molecule contains two hydrogen atomsand one oxygen atom. The arrangement of molecules in waterbecomes less orderly as water melts and more orderly as water freezes.

Melting In ice, attractions between water molecules keep the mol-ecules in fixed positions. When ice cubes are removed from a freezerand placed in an empty glass, heat flows from the air to the ice. As theice gains energy, the molecules vibrate more quickly. At the meltingpoint of water, 0°C, some molecules gain enough energy to overcomethe attractions and move from their fixed positions. When all the mol-ecules have enough energy to move, melting is complete. Any energygained by the water after the phase change increases the average kineticenergy of the molecules, and the temperature rises.

Freezing When liquid water is placed in a freezer, energy flowsfrom the water to the air in the freezer, and the water cools down. Asthe average kinetic energy of its molecules decreases, they move moreslowly. At the freezing point of water, some molecules move slowlyenough for the attractions between molecules to have an effect. Whenall the molecules have been drawn into an orderly arrangement, freez-ing is complete. Any energy removed from the ice after the phasechange decreases the average kinetic energy of the molecules, and thetemperature of the ice drops.

Often, people think of cold temperatures when theyhear the term freezing. But substances that are solids atroom temperature can freeze at temperatures that are quitehigh. For example, silicon freezes at 1412°C (2574°F). As acomparison, you can bake cookies at 177°C (350°F).

Vaporization and CondensationFigure 20 shows how food cools and stays cold in a refrig-erator. The process depends on a substance that changesfrom a liquid to a gas to a liquid over and over again.During these phase changes, energy flows from the insideof the refrigerator to the outside.

The phase change in which a substance changes froma liquid into a gas is vaporization. Vaporization is anendothermic process. That is, a substance must absorbenergy in order to change from a liquid to a gas. Onegram of water gains 2258 joules of energy when it vapor-izes at 100°C. This amount of energy is the heat ofvaporization for water. The heat of vaporization variesfrom substance to substance.

Figure 20 In a refrigerator, a pairof phase changes keep the foodcold. Energy from inside the foodcompartment is used to change aliquid to a gas in the evaporator.This energy is released when thecompressed gas changes back to aliquid in the condenser.

Energy removedfrom food

compartment

Energyreleased to

surroundings

Compressor

Condenser

Evaporator

For: Links on phases of matter

Visit: www.SciLinks.org

Web Code: ccn-1033

88 Chapter 3

Melting and FreezingUse VisualsFigure 20 Keeping food cool requiresthe transfer of energy. Ask, What changeoccurs in the evaporator? Is thischange exothermic or endothermic?(Liquid to gas; the change is endothermicbecause energy is absorbed from the foodcompartment) What change occurs in the condenser? Is this changeexothermic or endothermic? (Gas isliquid; the change is exothermic becauseenergy is released to the surroundings)Visual

FYIRefrigeration is also discussed in Chapter 16, where the focus is on theneed for work to be done for heat toflow from an area of lower temperatureto an area at higher temperature. In thischapter, the focus is on the endothermicand exothermic phase changes.

Vaporization andCondensationUse Community ResourcesInvite an appliance repairperson to cometo the class and speak about compoundsused in air conditioner and refrigeratorcooling coils. Suggest that the speakerdescribe the types of compounds used,how the compounds have changed overtime, and whether there are any problemswith the replacement compounds. Interpersonal

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Section 3.3 (continued)

Chlorofluorocarbons Under the Clean AirAct, which became effective in November of1995, it became illegal to release into the aircompounds that harm Earth’s ozone layer.Chlorofluorocarbons (CFCs) are among thebanned substances. CFCs were used as refrig-erants in cooling devices, such as refrigeratorsand air conditioners.

Because CFCs do not dissolve easily in waterand are generally not very reactive, they tendto stay in the atmosphere once they are

released. In the lower atmosphere, theirpresence causes few problems. However, thesecompounds move into the stratosphere wherethey are exposed to high energy radiation. Thisradiation causes the CFCs to react and releasechlorine atoms. These chlorine atoms reactwith oxygen to form chlorine monoxide, whichcauses the ozone to decompose into oxygen.Hydrogen fluorocarbons (HFCs) have replacedCFCs in many cooling devices.

Facts and Figures

Download a worksheet on phasesof matter for students to complete,and find additional teacher supportfrom NSTA SciLinks.

Scientists distinguish two vaporization processes—boiling and evaporation. Evaporation takes placeat the surface of a liquid and occurs at temperaturesbelow the boiling point.

Evaporation If you go outside after a rain showeron a sunny, warm day, you may notice puddles ofwater. If you return to the same location after a fewhours, the puddles may be gone. This disappearanceof the puddles is due to evaporation. Evaporation isthe process that changes a substance from a liquid to agas at temperatures below the substance’s boiling point.

Figure 21 shows what is happening as water evaporates from asmall, shallow container. Some molecules near the surface are movingfast enough to escape the liquid and become water vapor. (A vapor isthe gaseous phase of a substance that is normally a solid or liquid atroom temperature.) The greater the surface area of the container, thefaster the water evaporates.

What happens if the water is in a closed container? As the waterevaporates, water vapor collects above the liquid. The pressure causedby the collisions of this vapor and the walls of the container is calledvapor pressure. The vapor pressure of water increases as the tempera-ture increases. At higher temperatures, more water molecules haveenough kinetic energy to overcome the attractions of other moleculesin the liquid.

Boiling As you heat a pot of water, both the temperature and thevapor pressure of the water increase. When the vapor pressure becomesequal to atmospheric pressure, the water boils. The temperature atwhich this happens is the boiling point of water.

The kinetic theory explains what happens when water boils. As thetemperature increases, water molecules move faster and faster. Whenthe temperature reaches 100°C, some molecules below the surface ofthe liquid have enough kinetic energy to overcome the attraction ofneighboring molecules. Figure 22 shows that bubbles of water vaporform within the liquid. Because water vapor is less dense than liquidwater, the bubbles quickly rise to the surface. When they reach thesurface, the bubbles burst and release water vapor into the air.

How does the surface area of a liquid affect therate of evaporation?

89

Figure 22 Boiling takes place throughouta liquid. Applying Concepts Explain whythe temperature of water does not riseduring boiling.

Figure 21 Evaporation takesplace at the surface of a liquid.

Build Science SkillsDesigning Experiments The rate ofevaporation is affected by surface area.Ask students to design an experimentusing water in a beaker with gradationsto test this statement. Have studentsidentify the variables that will need to be controlled (type of liquid, volume of liquid, temperature of liquid, time).Ask, What will the manipulatedvariable be? (Surface area) What will the responding variable be? (Rate ofevaporation) How will you measure therate of evaporation? (One acceptableanswer is measuring the liquid level after a specified interval of time.) Allow studentsto conduct approved experiments andsummarize their results in a report. Verbal, Logical

Students often think that atoms andmolecules expand as the temperaturerises. Use water’s expansion when itfreezes to challenge this misconception.Explain that the space between watermolecules is greater in ice than in liquidwater because of the arrangement ofmolecules in ice. When ice melts, thespace between molecules decreases andthe volume decreases. Logical

FYIEventually, no more vapor can collectabove the liquid in a closed container.The water continues to evaporate, but some of the vapor condenses inreturn. This is an example of a dynamicequilibrium. Chemical (and physical)equilibrium is introduced in Chapter 7.

Water, especially tap water, containsdissolved gases such as oxygen andnitrogen. When water is heated, thesolubility of these gases in waterdecreases, which causes small bub-bles to form in heated water before it begins to boil.

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States of Matter 89

Answer to . . .

Figure 22 Energy absorbed by the system during boiling is used toovercome attractions among watermolecules.

The greater the surfacearea, the faster the

water evaporates.

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Observing Phase Changes

Materials250-mL Erlenmeyer flask, graduated cylinder,thermometer, dry ice

Procedure1. Pour 150 milliliters of water into a 250-mL

Erlenmeyer flask. Place a thermometer in theflask. CAUTION Wipe up any spilled water rightaway to avoid slips and falls.

2. Observe what happens after your teacher addsa small piece of dry ice to the flask. (Dry ice issolid carbon dioxide.) CAUTION Dry ice candamage skin on contact. Do not touch the dry ice.

3. Record the temperature of the water just afterthe dry ice is added and again after it is nolonger visible.

Analyze and Conclude1. Observing What happened when the dry ice

was added to the water?

2. Analyzing Data Did adding the dry icecause the water to boil? Explain your answer.

3. Inferring What was the source of thebubbles in the water?

4. Formulating Hypotheses What caused acloud to form above the flask?

5. Applying Concepts What phase changesoccurred in the flask?

Figure 23 Water vapor from theair condensed into drops of liquidwater on these blades of grass.

90 Chapter 3

The boiling point of a substance depends on the atmospheric pres-sure. The normal boiling point of water at sea level is 100°C. At higherelevations, the atmospheric pressure is lower. Do you know thatDenver, Colorado, is called the mile-high city? This nickname is basedon Denver’s location at one mile above sea level. In Denver, the vaporpressure of water will equal atmospheric pressure at temperaturesbelow 100°C. The boiling point of water in Denver can be as low as95°C. Food does not cook as quickly at 95°C as it does at 100°C. Pastatakes longer to cook in Denver than in New Orleans, Louisiana, a citythat is located near sea level.

Condensation Have you ever come out of a shower to find yourbathroom mirror clouded over? The “cloud” on the mirror is caused bywater vapor that cooled as it came in contact with the mirror. Thewater vapor transferred heat to the mirror and condensed into liquidwater. Condensation is the phase change in which a substance changesfrom a gas or vapor to a liquid. This process is also responsible for themorning dew on the blades of grass in Figure 23. Condensation is anexothermic process.

90 Chapter 3

Observing Phase Changes

Objective After completing this lab, students willbe able to • identify examples of condensation and

sublimation.

Skills Focus Observing

Prep Time 15 minutes

Advance Prep Obtain dry ice from a local supplier or from a scientificsupply house, ice cream wholesaler, or compressed gas dealer. Do not storedry ice in an airtight container. Leave awindow open in your car if you have dryice in the car. Use a hammer to carefullybreak the dry ice into pea-sized pieces.

Class Time 20 minutes

Safety Do not handle dry ice with barehands. It damages skin tissue on contact.Wear safety goggles, a lab apron, andleather gloves when handling dry ice. Use forceps to dispense a pea-sized pieceof dry ice into each flask. Caution studentsnot to touch dry ice and to use care whenhandling glassware to avoid breakage.Provide only nonmercury thermometers.

Teaching Tips• Do this lab after students have studied

sublimation.• If students are having trouble with

Question 2, ask at what temperaturewater boils. If they are having troublewith Question 4, remind them thatwater vapor exists above the liquid.

Expected Outcome When dry ice is added to water, vigorous bubblingbegins and a fog appears above the liquid.

For EnrichmentChallenge students to propose a way tohave solid, liquid, and gaseous watertogether in the same test tube. One wayis to place ice in liquid water in a closedcontainer. Water vapor will collect abovethe surface of the water. Visual, Logical

L3

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Section 3.3 (continued)

Analyze and Conclude1. Bubbles formed in the water, and a fogformed above the water. The temperature of thewater decreased.2. No, because the water was not at 100°C whenbubbles appeared.3. Carbon dioxide gas from the dry ice

4. Cold carbon dioxide gas chilled the air abovethe water, causing water vapor to condense intotiny liquid droplets.5. Sublimation of carbon dioxide and condensa-tion of water occurred. Students may also mentionvaporization of water. Logical, Kinesthetic

Section 3.3 Assessment

Reviewing Concepts1. Name six common phase changes.

2. What happens to the temperature of asubstance during a phase change?

3. How does the energy of a system changeduring a phase change?

4. What happens to the arrangement ofwater molecules as water melts and freezes?

5. What is the difference betweenevaporation and boiling?

6. Explain why sublimation and deposition areclassified as physical changes.

Critical Thinking 7. Applying Concepts How can the mass of a

pile of snow decrease on a sunny day whenthe air temperature does not rise above 0°C?

8. Drawing Conclusions At room temperature,table salt is a solid and acetone is a liquid.Acetone is the main ingredient in nail polishremover. What conclusion can you draw aboutthe melting points of these materials?

Sublimation and Deposition Directors of concerts and plays sometimes use dry ice to create afog-like special effect. Dry ice is the common name for the solidform of carbon dioxide. At room temperature, dry ice can directlychange from a solid to a colorless gas. Sublimation is the phasechange in which a substance changes from a solid to a gas or vaporwithout changing to a liquid first. Sublimation is an endothermicchange. As dry ice sublimes, the cold carbon dioxide vapor causeswater vapor in the air to condense and form clouds.

Where does the name dry ice come from? Solid carbon dioxidedoes not form a liquid as its temperature rises. Suppose 100 steaksare shipped from Omaha, Nebraska, to a supermarket in Miami,Florida. The steaks will spoil unless they are kept cold during thetrip. If regular ice is used, water collects in the shipping containeras the ice melts. If the steaks are shipped in dry ice, the containerand the steaks stay dry during the journey. Figure 24 shows anotheruse of dry ice.

When a gas or vapor changes directly into a solid without firstchanging to a liquid, the phase change is called deposition. Thisexothermic phase change is the reverse of sublimation. Depositioncauses frost to form on windows. When water vapor in the air comesin contact with cold window glass, the water vapor loses enoughkinetic energy to change directly from a gas to a solid.

States of Matter 91

Steps in a Process Write a paragraphdescribing three steps that must occur for awater molecule to start on the surface of hotbath water and end up on the surface of abathroom mirror. Note whether the phasechanges that take place during the processare endothermic or exothermic. (Hint: Usewords such as first, next, and finally to showthe order of events.)

Figure 24 A technician at TinkerAir Force Base in Oklahoma hangsa mosquito trap. The trap is baitedwith dry ice because mosquitoesare attracted to carbon dioxide.

Sublimation andDepositionUse VisualsFigure 24 Have students examineFigure 24. Explain that the trap was hung as part of a study of West Nile virus,a mosquito-borne disease. Mosquitoesacquire the virus from infected birds andthen transmit the virus to other animalsand humans. Mosquitoes are collectedand sent to a laboratory for identificationby species and gender. Samples of similarfemale mosquitoes are blended and theirRNA is analyzed for West Nile virus. Ask,Why is dry ice used to bait the mos-quito trap rather than gaseous carbondioxide? (The large amount of carbondioxide stored in dry ice is released slowlyover time rather than all at once.)Logical

ASSESSMENTEvaluate UnderstandingHave students write the six terms thatdescribe phase changes. Next to eachterm, students should describe the typeof change. For example, for melting,students would indicate that the phasechange is from a solid to a liquid. Tellstudents to include arrows pointing upto identify exothermic changes andarrows pointing down to identifyexothermic changes.

ReteachUse Figure 16 to review the six phasechanges described in this section. Ask,What do the phase changes with redarrows have in common? (They are allexothermic processes.) What do thephase changes with blue arrows havein common? (They are all endothermicprocesses.)

First, the water molecule on the surfaceof the bath water evaporates—anendothermic change. Next, randommotion of the molecule carries it to the surface of the mirror. Finally, themolecule condenses on the mirror—an exothermic change.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 3.3.

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States of Matter 91

5. Evaporation takes place at the surface of aliquid and occurs at temperatures below theboiling point. 6. A substance’s identity does not changeduring sublimation or deposition.7. When snow absorbs energy from sunlight,it either melts or sublimes.8. Table salt must have a melting point aboveroom temperature, and acetone must have amelting point below room temperature.

Section 3.3 Assessment

1. Melting, freezing, vaporization,condensation, sublimation, and deposition2. The temperature of a substance does notchange during a phase change.3. Energy is either released or absorbed duringa phase change.4. The arrangement of molecules becomes lessorderly as water melts and more orderly aswater freezes.

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66 Chapter 3

States of MatterC H A P T E R

When temperatures rise in the spring, the �ice begins to melt on Bow Lake at BanffNational Park in Alberta, Canada.

How do science concepts apply to yourworld? Here are some questions you’ll beable to answer after you read this chapter.

■ How can balloons have many different shapes?(Section 3.1)

■ Why should you check the air pressure of tires before you go for a long drive? (Section 3.2)

■ What controls the movement of air into and out of your lungs as you breathe? (Section 3.2)

■ How is the altitude of a hot-air balloon controlled? (page 82)

■ Why does pasta take longer to cook in Denver than in New Orleans? (Section 3.3)

ASSESS PRIORKNOWLEDGEUse the Chapter Pretest below to assessstudents’ prior knowledge. As needed,review these Science Concepts andMath Skills with students.

Review Science ConceptsSection 3.1 Review density, puresubstances, homogeneous mixtures, andheterogeneous mixtures with students.Students may refer to the graphic orga-nizer they completed in Section 2.1.

Section 3.2 Encourage students toreview scientific methods, includingforming and testing hypotheses. Discusshow developing a hypothesis is animportant step in a scientific method.

Section 3.3 Have students review SI units for temperature and volume.

Review Math SkillsFormulas and Equations Students will need to know how to write equationsand solve them for unknowns in order tosolve problems involving gas laws.

Direct students to the Math Skills in theSkills and Reference Handbook at theend of the student text.

CHEMISTRY

Chapter 3

Chapter Pretest

1. What is the density of a sample whosemass is 12.02 g and whose volume is 6.01 mL? (2.00 g/mL)2. Which of the following is an element? (c)

a. Sand b. Waterc. Gold d. Sugar

3. Differentiate heterogeneous from homo-geneous mixtures. (Heterogeneous mixture:parts are noticeably different; homogeneousmixture: parts are difficult to distinguish)

4. Which of the following is not a step in ascientific method? (b)

a. Developing a procedure to test ahypothesis

b. Drawing a conclusion without anysupporting evidence

c. Forming a testable hypothesisd. Making observations

5. Identify tools needed to measure temp-erature and length. (Thermometer and ruler)

6. True or False: All of the following units areSI units: meter, pound, and kelvin. (False)7. Density, mass, and volume are related by the equation density � mass/volume.What equation would you use to findvolume if you knew the density and mass?(volume � mass/density)8. Bromine boils at a temperature of 58.63ºC.What is this temperature in kelvins? (331.78 K)

66 Chapter 3

CHEMISTRY

3.1 Solids, Liquids, and Gases

3.2 The Gas Laws

3.3 Phase Changes

Chapter Preview

Video Field Trip

Up, Up, and Away

How Easy Is It to Compress Air and Water?Procedure1. Insert a plunger into a syringe that is sealed at

the narrow end. Push the plunger into thesyringe as far as you can. Use the marks onthe side of the syringe to read the volume ofthe air inside the syringe. Record this volume.

2. Remove the plunger. Fill the syringe with waterby holding it under water in a large plasticcontainer of water. CAUTION Wipe up anyspilled water right away to avoid slips and falls.

3. While holding the syringe over the container,repeat Step 1. Record the volume of the water.

Think About It1. Comparing and Contrasting Which was

harder to compress, the air or the water?(To compress means to squeeze into asmaller volume.)

2. Inferring Based on your answer toQuestion 1, in which material are theparticles closer together, in air or inwater? Explain your answer.

States of Matter 67

How Easy Is It to Compress Air and Water?Purpose In this activity, students will infer that gases are more easilycompressed than liquids because there is more space between the particles in agas than between the particles in a liquid.

Skills Focus Comparing

Prep Time 5 minutes

Materials syringe (sealed at narrowend), water

Advance Prep Obtain syringes from ascientific supply company. Remove theneedles and seal the tip of each syringeby removing the plunger and droppingsome nonwater-soluble glue into thehead of the syringe.

Class Time 15 minutes

Safety Students should wear safetygoggles and lab aprons.

Teaching Tips • To keep track of the syringes, number

them with an indelible marker beforedistributing them to students. As youdistribute, record the syringe numberand student’s name. When you retrievethe syringes, check against the list.

• Demonstrate the proper handling ofthe syringe and plunger. Showstudents how to correctly read themarkings on the syringes.

• Separate the plungers from thesyringes before distributing them.

• Separate the plungers from thesyringes, rinse them with distilledwater, and allow them to air-drybefore storing them.

Expected Outcome The plunger will be pushed farther into the air-filledsyringe than into the water-filled syringe.

Think About It1. The water was harder to compress. 2. The particles are closer together inwater. Air can be compressed moreeasily than water because there is morespace between the particles in air.Visual, Logical

L2

States of Matter 67

Encourage students to view the Video Field Trip“Up, Up, and Away.”

ENGAGE/EXPLORE

Video Field Trip

Up, Up, and Away

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92 Chapter 3

Lauric acid is a solid that is found in coconuts andprocessed foods that are made with coconut oil.Lauric acid is also used to make some soaps andcosmetics. In this lab, you will measure thetemperature of ice and of lauric acid as these solidsare heated and melt. You will graph the data youcollect and compare the heating curves for ice andlauric acid.

Problem What happens to the temperatureof a substance during a phase change?

Materials• 500-mL beaker• crushed ice• thermometer• hot plate• clock with second hand• test tube of lauric acid with thermometer• glass stirring rod• graph paper

For the probeware version of this lab, seethe Probeware Lab Manual, Lab 1.

Skills Measuring, Using Graphs

Procedure

Part A: Heating Ice1. On a sheet of paper, make a copy of the data

table shown. Start with 11 blank rows, butleave space below your data table to add morerows, if necessary.

2. Fill a 500-mL beaker halfway with crushed ice.CAUTION Use care when handling glassware toavoid breakage. Wipe up any spilled ice rightaway to avoid slips and falls.

3. Place the beaker on a hot plate. Don’t turn thehot plate on yet. Insert a thermometer into theice. Because it takes several seconds for thethermometer to adjust to the temperature ofits surroundings, wait 20 seconds and thenmeasure the temperature of the ice. Recordthis temperature next to the 0 minutes entryin your data table.

4. Turn the hot plate to a low setting. CAUTION Be careful not to touch the hot platebecause contact with the hot plate could cause a burn.

5. Observe and record the temperature at one-minute intervals until all the ice has changedto liquid water. Circle the temperature atwhich you first observe liquid water and thetemperature at which all the ice has changedto liquid water.

Data Table

01

Temperature ofWater (�C)

Time(minutes)

Temperature ofLauric Acid (�C)

Investigating Changes in Temperature During Heating of Solids

92 Chapter 3

Investigating Changes in Temperature During Heating of SolidsObjectiveAfter completing this activity, studentswill be able to• explain the constant temperature of a

substance that is undergoing a phasechange.

Students might think the temperatureshould keep increasing as the ice melts.Ask them to predict the shape of themelting curve. After performing the lab,ask students to compare theirpredictions to the actual curves.

Skills Focus Measuring, UsingTables and Graphs

Prep Time 30 minutes

Advance Prep Buy crushed ice orcrush it by placing ice cubes into aplastic bag and hitting them with amallet while wearing goggles. Pourgranular lauric acid into the test tubesand insert a thermometer into each testtube. Rather than discarding the lauricacid after the first class, leave thethermometers in the test tubes andallow the test tubes to cool to roomtemperature. The thermometers will beembedded in the solidified lauric acid.

Class Time 45 minutes

Safety Provide only nonmercurythermometers. Position hot plates awayfrom the edges of tables. Place powercords behind the hot plates, where theyare not likely to become entangled witharms or clothing. Once a hot plate isturned on, students should not touch it.

Teaching Tips • Emphasize the importance of making

an accurate measurement of the initialtemperature of the ice.

• You may wish to save time by havingsome students perform Part A of thelab and others perform Part B.Students can then exchange databefore making their graphs.

• To help students construct theirgraphs, show a sample graph on anoverhead transparency. Include thegrids for the horizontal and verticalaxes, but not the data.

• You may wish to postpone thegraphing of the results of Part A (Step 7) to the end of the lab, after all data have been collected.

L2

Probeware Lab Manual Versions of thislab for use with probeware available fromPasco, Texas Instruments, and Vernier are inthe Probeware Manual.

States of Matter 93

Analyze and Conclude1. Using Graphs Describe the shape of your

graph for ice.

2. Analyzing Data What happened to thetemperature of the ice-water mixture duringthe phase change?

3. Drawing Conclusions What happened tothe energy that was transferred from the hotplate to the ice during the phase change?

4. Comparing and Contrasting Compare the shapes of the graphs for ice and for lauricacid. Compare the melting points of ice andlauric acid.

For: Data sharing

Visit: PHSchool.com

Web Code: ccd-1030

6. After all the ice has melted, make five moremeasurements of the temperature at one-minute intervals. Turn off the hot plate.

7. Graph your data with time on the horizontalaxis and temperature on the vertical axis.

Part B: Heating Lauric Acid8. Empty the water from the beaker into the sink.

Fill the beaker halfway with cool tap water.

9. Place a test tube containing lauric acid anda thermometer into the beaker. If necessary,add or remove water from the beaker so thatthe surface of the water is above the surfaceof the lauric acid but below the opening ofthe test tube.

10. Place the beaker on the hot plate. After 20 seconds, measure the temperature of thelauric acid. Record this temperature next tothe 0 minutes entry in your data table.

11. Repeat Steps 4 through 7 using the lauric acidinstead of the ice. To keep the temperature thesame throughout the water bath, use the glassstirring rod to stir the water after you takeeach temperature measurement.

Expected Outcome In Part A, if thereadings are taken quickly enough, thefirst few temperature readings may bebelow 0°C. The temperature readingsshould remain at 0°C until all the ice hasmelted. The temperature should begin to rise once the ice has melted. Heatingsolid lauric acid raises its temperature toits melting point of 43.2°C. The tempera-ture will begin to rise again after thelauric acid has melted.

Sample Data

Analyze and Conclude1. The graph rises quickly to 0°C andremains horizontal at that temperaturefor a number of minutes. Then, it beginsto rise again. 2. The temperature remained constantuntil the phase change was completed. 3. At first, the energy absorbed by theice was used to overcome the forces ofattraction holding water molecules infixed positions. After all of the ice hadmelted, the energy absorbed increasedthe kinetic energy of the molecules inthe liquid water.4. The two graphs had similar shapes.However, ice melted at 0�C and lauricacid melted at about 43�C.Logical

States of Matter 93

Time (min)

Lauric acid

Water

Tem

per

atu

re (

ßC

)

80

60

40

0

20

-200 5 15 252010

Typical Melting Curves

Have students pool and comparetheir data with students nationwideby visiting the Prentice Hall Website at www.PHSchool.com.

0066_hsps09te_Ch03.qxp 4/18/07 10:40 AM Page 93

66A Chapter 3

Planning Guide

SECTION OBJECTIVES STANDARDS ACTIVITIES and LABSNATIONAL STATE

A-1, B-2, B-5,F-5, G-1, G-2,G-3

3.1 Solids, Liquids, and Gases, pp. 68–74

1 block or 2 periods

3.1.1 Describe the five states of matter.

3.1.2 Classify materials as solids, liquids, orgases.

3.1.3 Explain the behavior of gases, liquids,and solids, using kinetic theory.

SE Inquiry Activity: How Easy Is It toCompress Air and Water? p. 67

TE Teacher Demo: Comparing LiquidVolume, p. 69

TE Teacher Demo: Detecting the Motion of a Gas, p. 72

LM Investigation 3B: Measuring SpacesBetween Particles of Matter L1

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Easy Planner Teacher Express

3.2 The Gas Laws, pp. 75–81

1 block or 2 periods

3.2.1 Define pressure and gas pressure.

3.2.2 Identify factors that affect gas pressure.

3.2.3 Predict changes in gas pressure due tochanges in temperature, volume, andnumber of particles.

3.2.4 Explain Charles’s law, Boyle’s law, andthe combined gas law.

3.2.5 Apply gas laws to solve problemsinvolving gases.

A-1, A-2, B-2,B-4, B-5, G-1,G-2, G-3

SE Quick Lab: Observing the Effect of Temperature on Gas Pressure,p. 79

TE Build Science Skills: Observing,p. 75

TE Teacher Demo: Changing Volume of a Balloon, p. 76 L2

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3.3 Phase Changes, pp. 84–91

1 block or 2 periods

3.3.1 Describe phase changes.

3.3.2 Explain how temperature can be used torecognize a phase change.

3.3.3 Explain what happens to the motion,arrangement, and average kinetic energyof water molecules during phase changes.

3.3.4 Describe each of the six phase changes.

3.3.5 Identify phase changes as endothermicor exothermic.

A-1, A-2, B-2,B-5

SE Quick Lab: Observing Phase Changes, p. 90

SE Exploration Lab: Investigating Changes in Temperature During Heating of Solids, pp. 92–93

TE Teacher Demo: Energy Transfer,p. 86

LM Investigation 3A: Performing aFractional Distillation L2

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