chapter 1

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Chapter 1M atter and

Energy

Tro's "Introductory Chemistry", Chapter 1

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What Is Chemistry?

What chemists try to do is discover the relationships between the particle structure of matter and the properties of matter we observe.Chemistry is the science that seeks to understand what matter does by studying what atoms and molecules do.


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Structure Determines PropertiesEverything is made of tiny pieces called atoms and molecules.Chemists believe that the properties of a substance are determined by the kinds, numbers, and relationships between these pieces.


4

The Scientific Method

ObservationFormulate a QuestionPattern RecognitionDevelop a HypothesisExperimentationSummarize Information


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What Is a Measurement?

Quantitative observation.Comparison to an agreed upon standard.Every measurement has a number and a unit.


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A Measurement

The unit tells you to what standard you are comparing your object. The number tells you:1.What multiple of the standard the object

measures.2. The uncertainty in the measurement.

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Scientists have measured the average global temperature rise over the past

century to be 0.6 °C

°C tells you that the temperature is being compared to the Celsius temperature scale.0.6 tells you that:

1. The average temperature rise is 0.6 times the standard unit of 1 degree Celsius.

2. The confidence in the measurement is such that we are certain the measurement is between 0.5 and 0.7 °C.

Tro's Introductory Chemistry, Chapter 2

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Scientific Notation

A way of writing large and small numbers.


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Big and Small Numbers

We commonly measure objects that are many times larger or smaller than our standard of comparison.Writing large numbers of zeros is tricky and confusing.

-digit limit of your calculator!

diameter is1,392,000,000 m.

average diameter is0.000 000 000 3 m.


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Scientific Notation

Each decimal place in our number system represents a different power of 10.Scientific notation writes the numbers so they are easily comparable by looking at the power of 10.

diameter is1.392 x 109 m.

average diameter is3 x 10-10 m.


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123401. Locate the decimal point.

12340.2. Move the decimal point to obtain a number between 1 and 10.

1.2343. Multiply the new number by 10n .

Where n is the number of places you moved the decimal point.

1.234 x 104

4. If you moved the decimal point to the left, then n is +; if you moved it to the right, then n is .

1.234 x 104

Writing a Number in Scientific Notation, Continued


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Writing a Number in Scientific Notation, Continued0.00012340

1. Locate the decimal point.0.00012340

2. Move the decimal point to obtain a number between 1 and 10.1.2340

3. Multiply the new number by 10n .Where n is the number of places you moved the decimal point.

1.2340 x 104

4. If you moved the decimal point to the left, then n is +; if you moved it to the right, then n is .

1.2340 x 10-4

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Writing a Number in Standard Form1.234 x 10-6

Since exponent is -6, make the number smaller by moving the decimal point to the left 6 places.

When you run out of digits to move around, add zeros.Add a zero in front of the decimal point for decimal numbers.

000 001.2340.000 001 234


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Practice Write the Following in Scientific Notation

123.4

145000

25.25

1.45

8.0012

0.00234

0.0123

0.000 008706


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Practice Write the Following in Scientific Notation, Continued

123.4 = 1.234 x 102

145000 = 1.45 x 105

25.25 = 2.525 x 101

1.45 = 1.45 x 100

8.0012 = 8.0012 x 100

0.00234 = 2.34 x 10-3

0.0123 = 1.23 x 10-2

0.000 008706 = 8.706 x 10-6


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Practice Write the Following in Standard Form

2.1 x 103

9.66 x 10-4

6.04 x 10-2

4.02 x 100

3.3 x 101

1.2 x 100


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Practice Write the Following in Standard Form, Continued

2.1 x 103 = 2100

9.66 x 10-4 = 0.000966

6.04 x 10-2 = 0.0604

4.02 x 100 = 4.02

3.3 x 101 = 33

1.2 x 100 = 1.2Tro's "Introductory Chemistry",

Chapter 218

Inputting Scientific Notation into a CalculatorInput the decimal part of the number.

If negative press +/-key.

( ) on some.

Press EXP.EE on some.

Input exponent on 10.Press +/- key to change exponent to negative.

-1.23 x 10-3

-1.23 -03 Press +/-

Input 1.23 1.23

Press EXP -1.23 00

Input 3 -1.23 03

-1.23 Press +/-

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Significant Figures

Writing numbers to reflect precision.


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Exact Numbers vs. MeasurementsSometimes you can determine an exact value for a quality of an object.

Often by counting.Pennies in a pile.

Sometimes by definition1 ounce is exactly 1/16th of 1 pound.

Whenever you use an instrument to compare a quality of an object to a standard, there is uncertainty in the comparison.


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Reporting MeasurementsMeasurements are written to indicate the uncertainty in the measurement.The system of writing measurements we use is called significant figures.When writing measurements, all the digits written are known with certainty except the last one, which is an estimate.

45.872

CertainEstimated

45.872


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Estimating the Last DigitFor instruments marked with a scale, you get the last digit by estimating between the marks.

If possible.Mentally divide the space into 10 equal spaces, then estimate how many spaces over the indicator is. 1.2 grams


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Skillbuilder 2.3 Reporting the Right Number of Digits

A thermometer used to measure the temperature of a backyard hot tub is shown to the right. What is the temperature reading to the correct number of digits?


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Skillbuilder 2.3 Reporting the Right Number of Digits

A thermometer used to measure the temperature of a backyard hot tub is shown to the right. What is the temperature reading to the correct number of digits?

103.4 °F

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Significant FiguresThe non-placeholding digits in a reported measurement are called significant figures.

Some zeros in a written number are only there to help you locate the decimal point.

Significant figures tell us the range of values to expect for repeated measurements.

The more significant figures there are in a measurement, the smaller the range of values. Therefore, the measurement is more precise.

12.3 cmhas 3 significant

figures and its range is12.2 to 12.4 cm.

12.30 cmhas 4 significant

figures and its range is

12.29 to 12.31 cm.


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Counting Significant Figures

All non-zero digits are significant.1.5 has 2 significant figures.

Interior zeros are significant.1.05 has 3 significant figures.

Trailing zeros after a decimal point are significant.

1.050 has 4 significant figures.


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Counting Significant Figures, Continued

Leading zeros are N O T significant.0.001050 has 4 significant figures.

1.050 x 10-3

Zeros at the end of a number without a written decimal point are ambiguous and should be avoided by using scientific notation.

If 150 has 2 significant figures, then 1.5 x 102,but if 150 has 3 significant figures, then 1.50 x 102.


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Significant Figures and Exact NumbersExact numbers have an unlimited number of significant figures. A number whose value is known with complete certainty is exact.

From counting individual objects.From definitions.

1 cm is exactly equal to 0.01 m.From integer values in equations.

In the equation for the radius of a circle, the 2 is exact.

radius of a circle = diameter of a circle2


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Determine the Number of Significant Figures, the Expected Range of Precision, and Indicate

the Last Significant Figure 12000

120.

12.00

1.20 x 103

0.0012

0.00120

1201

1201000


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12000 2

120. 3

12.00 4

1.20 x 103 3

0.0012 2

0.00120 3

1201 4

1201000 4

Determine the Number of Significant Figures, the Expected Range of Precision, and Indicate

the Last Significant Figure, Continued

From 11000 to 13000.

From 119 to 121.

From 11.99 to 12.01.

From 1190 to 1210. From 1200000 to 1202000.

From 1200 to 1202.

From 0.0011 to 0.0013.

From 0.00119 to 0.00121.

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Multiplication and Division with Significant Figures

When multiplying or dividing measurements with significant figures, the result has the same number of significant figures as the measurement with the fewest number of significant figures.

5.02 89,665 0.10 = 45.0118 = 453 sig. figs. 5 sig. figs. 2 sig. figs. 2 sig. figs.

5.892 6.10 = 0.96590 = 0.9664 sig. figs. 3 sig. figs. 3 sig. figs.


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RoundingWhen rounding to the correct number of significant figures, if the number after the place of the last significant figure is:

1. 0 to 4, round down.Drop all digits after the last significant figure and leave the last significant figure alone.Add insignificant zeros to keep the value, if necessary.

2. 5 to 9, round up.Drop all digits after the last significat figure and increase the last significant figure by one.Add insignificant zeros to keep the value, if necessary.


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Rounding, ContinuedRounding to 2 significant figures.2.34 rounds to 2.3.

Because the 3 is where the last significant figure will be and the number after it is 4 or less.

2.37 rounds to 2.4.Because the 3 is where the last significant figure will be and the number after it is 5 or greater.

2.349865 rounds to 2.3.Because the 3 is where the last significant figure will be and the number after it is 4 or less.


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Rounding, Continued0.0234 rounds to 0.023 or 2.3 10-2.


0.0237 rounds to 0.024 or 2.4 10-2.Because the 3 is where the last significant figure will be and the number after it is 5 or greater.

0.02349865 rounds to 0.023 or 2.3 10-2.Because the 3 is where the last significant figure will be and the number after it is 4 or less.


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Rounding, Continued234 rounds to 230 or 2.3 102 .


237 rounds to 240 or 2.4 102 .Because the 3 is where the last significant figure will be and the number after it is 5 or greater.

234.9865 rounds to 230 or 2.3 102 .Because the 3 is where the last significant figure will be and the number after it is 4 or less.


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Determine the Correct Number of Significant Figures for Each Calculation and

Round and Report the Result1. 1.01 0.12 53.51 96 = 0.067556

2. 56.55 0.920 34.2585 = 1.51863

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Round and Report the Result, Continued1. 1.01 0.12 53.51 96 = 0.067556 = 0.068

2. 56.55 0.920 34.2585 = 1.51863 = 1.52

3 sf 2 sf 4 sf 2 sf Result should have 2 sf.

7 is in place of last sig. fig., number after

is 5 or greater, so round up.

4 sf 3 sf 6 sf Result should have 3 sf.




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Addition and Subtraction with Significant Figures

When adding or subtracting measurements with significant figures, the result has the same number of decimal places as the measurement with the fewest number of decimal places.

5.74 + 0.823 + 2.651 = 9.214 = 9.212 dec. pl. 3 dec. pl. 3 dec. pl. 2 dec. pl.

4.8 - 3.965 = 0.835 = 0.81 dec. pl 3 dec. pl. 1 dec. pl.


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Round and Report the Result1. 0.987 + 125.1 1.22 = 124.867

2. 0.764 3.449 5.98 = -8.664


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Round and Report the Result, Continued1. 0.987 + 125.1 1.22 = 124.867 = 124.9

2. 0.764 3.449 5.98 = -8.664 = -8.66

3 dp 1 dp 2 dp Result should have 1 dp.



3 dp 3 dp 2 dp Result should have 2 dp.

6 is in place of last sig. fig., number after is 4 or less,

so round down.


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Both Multiplication/Division and Addition/Subtraction with

Significant FiguresWhen doing different kinds of operations with measurements with significant figures, evaluate the significant figures in the intermediate answer, then do the remaining steps.Follow the standard order of operations.

Please Excuse My Dear Aunt Sally.

3.489 (5.67 2.3) =2 dp 1 dp

3.489 3.37 = 124 sf 1 dp & 2 sf 2 sf

- n


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Example 1.6 Perform the Following Calculations to the Correct Number of Significant Figures

4555.30015.45120.010.1 a)

5820.1001.105355.0

33.4526755.45299870.3562.4 c)

02.855.084.14 d)

b)

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Example 1.6 Perform the Following Calculations to the Correct Number of Significant Figures,

Continued652.065219.04555.30015.45120.010.1 a)

4.9 8730.4

5820.1001.105355.0

5379904.5233.4526755.45299870.3562.4 c)

1.0142.002.855.084.14 d)

b)


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Basic Units of Measure


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UnitsUnits tell the standard quantity to which we are comparing the measured property.

Without an associated unit, a measurement is without meaning.

Scientists use a set of standard units for comparing all our measurements.

So we can easily compare our results.

Each of the units is defined as precisely as possible.


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The Standard UnitsScientists generally report results in an agreed upon International System.The SI System

Aka Système Internat ional

Quantity Unit SymbolLength meter mMass kilogram kgTime second sTemperature kelvin K


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Some Standard Units in the Metric System

Quantity M easured

Name of Unit

Abbreviation

Mass gram gLength meter mVolume liter LTime seconds sTemperature Kelvin K


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Experimental QuantitiesMass = amount of matter in an object

Measured in kilograms (kg)Weight = force of gravity on an objectweight = mass x acceleration due to gravity

Length = distance between two pointsMeasured in meters (m)

Volume = space occupied by an objectMeasured in liters (L)Remember that 1 mL = 1 cm3

Time measured in seconds (s)

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Common Prefixes in the SI System

Pre fix SymbolDe cimal

Equivale ntPowe r of 10

mega- M 1,000,000 Base x 106

kilo- k 1,000 Base x 103

deci- d 0.1 Base x 10-1

centi- c 0.01 Base x 10-2

milli- m 0.001 Base x 10-3

micro- or mc 0.000 001 Base x 10-6

nano- n 0.000 000 001 Base x 10-9


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Common Units and Their Equivalents

Length1 kilometer (km) = 0.6214 mile (mi)

1 meter (m) = 39.37 inches (in.)1 meter (m) = 1.094 yards (yd)

1 foot (ft) = 30.48 centimeters (cm)1 inch (in.) = 2.54 centimeters (cm) exactly


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Common Units and Their Equivalents, Continued

Volume1 liter (L) = 1000 milliliters (mL)1 liter (L) = 1000 cubic centimeters (cm3)1 liter (L) = 1.057 quarts (qt)

1 U.S. gallon (gal) = 3.785 liters (L)

M ass1 kilogram (km) = 2.205 pounds (lb)

1 pound (lb) = 453.59 grams (g)1 ounce (oz) = 28.35 (g)


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Problem Solving and Dimensional Analysis

Many problems in chemistry involve using relationships to convert one unit of measurement to another.Conversion factors are relationships between two units.

May be exact or measured.Both parts of the conversion factor have the same number of significant figures.

Conversion factors generated from equivalence statements.

e.g., 1 inch = 2.54 cm can give or in1cm54.2

cm54.2in1


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Problem Solving and Dimensional Analysis, ContinuedArrange conversion factors so the starting unit cancels.

Arrange conversion factor so the starting unit is on the bottom of the conversion factor.

May string conversion factors.So we do not need to know every relationship, as long as we can find something else the starting and desired units are related to :

unit desired unit re latedunit desired

unitsta rt unit re lated

unitsta rt

unit desired unitsta rt

unit desiredunitsta rt


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DensityRatio of mass:volume.Its value depends on the kind of material, not the amount.Solids = g/cm3

1 cm3 = 1 mLLiquids = g/mLGases = g/LVolume of a solid can be determined by water displacement Archimedes Principle.Density : solids > liquids > gases

Except ice is less dense than liquid water!

VolumeMassDensity

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Density as a Conversion Factor

Can use density as a conversion factor between mass and volume!

Density of H2O = 1 g/mL 1 g H2O = 1 mL H2ODensity of Pb = 11.3 g/cm3 11.3 g Pb = 1 cm3 Pb

How much does 4.0 cm3 of lead weigh?

=4.0 cm3 Pb 11.3 g Pb 1 cm3 Pb

45 g Pbx


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What Is Matter?M atter is defined as anything that occupies space and has mass.Even though it appears to be smooth and continuous, matter is actually composed of a lot of tiny little pieces we call atoms and molecules.


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Atoms and Molecules

Atoms are the tiny particles that make up all matter.In most substances, the atoms are joined together in units called molecules.

The atoms are joined in specific geometric arrangements.

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Structure Determines PropertiesThe properties of matter are determined by the atoms and molecules that compose it.

1. Composed of one carbon atom and two oxygen atoms.

2. Colorless, odorless gas.3. Incombustible.4. Does not bind to hemoglobin.

Carbon Dioxide1. Composed of one carbon atom

and one oxygen atom.2. Colorless, odorless gas.3. Burns with a blue flame.4. Binds to hemoglobin.

Carbon Monoxide


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Classifying Matterby Physical State

Matter can be classified as solid, liquid, or gas based on what properties it exhibits.

State Shape Volume Compress F low Solid Fixed Fixed No No

L iquid Indefinite Fixed No Yes

Gas Indefinite Indefinite Yes Yes

Indefinite = Takes the property of the container.60

Structure Determines PropertiesThe atoms or molecules have different structures in solids, liquids, and gases leading to different properties.

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SolidsThe particles in a solid are packed close together and are fixed in position.

Although they may vibrate.The close packing of the particles results in solids being incompressible.The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container and prevents the particles from flowing. Tro's "Introductory Chemistry",

Chapter 362

Solids, ContinuedSome solids have their particles arranged in an orderly geometric pattern we call these crystalline solids.

Salt and diamonds.Other solids have particles that do not show a regular geometric pattern over a long range we call these amorphous solids.

Plastic and glass.


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LiquidsThe particles in a liquid are closely packed, but they have some ability to move around. The close packing results in liquids being incompressible.The ability of the particles to move allows liquids to take the shape of their container

enough freedom to escape and expand to fill the container.


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Gases

In the gas state, the particles have complete freedom from each other.The particles are constantly flying around, bumping into each other and the container.In the gas state, there is a lot of empty space between the particles.

On average.


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Gases, ContinuedBecause there is a lot of empty space, the particles can be squeezed closer together. Therefore, gases are compressible.Because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container, and will flow.


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Atoms and MoleculesAtoms

Are submicroscopic particles that are the unit pieces of elements.Are the fundamental building blocks of all matter.

M oleculesAre submicroscopic particles that are the unit pieces of compounds. Two or more atoms attached together.

Attachments are called bonds.Attachments come in different strengths.

Molecules come in different shapes and patterns.

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Classifying Matter


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Properties of MatterPhysical P rope rties are the characteristics of matter that can be changed without changing its composition.

Characteristics that are directly observable.

C hemical P rope rties are the characteristics that determine how the composition of matter changes as a result of contact with other matter or the influence of energy.

Characteristics that describe the behavior of matter.


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Some Physical PropertiesMass Volume Density

Solid Liquid Gas

Melting point Boiling point Volatility

Taste Odor Color

Texture Shape Solubility

Electrical conductance

Thermal conductance

Magnetism

Malleability Ductility Specific heat capacity


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Some Physical Properties of IronIron is a silvery solid at room temperature with a metallic taste and smooth texture.Iron melts at 1538 °C and boils at 4428 °C.

3.Iron can be magnetized.Iron conducts electricity, but not as well as most other common metals.

average for a metal.It requires 0.45 J of heat energy to raise the temperature of one gram of iron by 1°C.


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Some Chemical Properties

Acidity Basicity (aka alkalinity) Causticity Corrosiveness Reactivity Stability Inertness Explosiveness (In)Flammability Combustibility Oxidizing ability Reducing ability


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Some Chemical Properties of IronIron is easily oxidized in moist air to form rust.When iron is added to hydrochloric acid, it produces a solution of ferric chloride and hydrogen gas.Iron is more reactive than silver, but less reactive than magnesium.

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Prac tice Decide Whe the r Each of the Obse rvations About Table Salt Is a Physical or C hemical P rope rty

Salt is a white, granular solid.Salt melts at 801 °C.Salt is stable at room temperature, it does not decompose.36 g of salt will dissolve in 100 g of water. Salt solutions and molten salt conduct electricity.When a clear, colorless solution of silver nitrate is added to a salt solution, a white solid forms.When electricity is passed through molten salt, a gray metal forms at one terminal and a yellow-green gas at the other.


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Prac tice Dec ide Whe the r Each of the Obse rvations About Table Salt Is a Physical or C hemical P rope rty

Salt is a white, granular solid = physical.Salt melts at 801 °C = physical.Salt is stable at room temperature, it does not decompose = chemical.36 g of salt will dissolve in 100 g of water = physical.Salt solutions and molten salt conduct electricity = physical.When a clear, colorless solution of silver nitrate is added to a salt solution, a white solid forms = chemical.When electricity is passed through molten salt, a gray metal forms at one terminal and a yellow-green gas at the other = chemical.


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Changes in Matter, ContinuedPhysical Changes Changes in the properties of matter that do not effect its composition.

Heating water. Raises its temperature, but it is still water.

Evaporating butane from a lighter.Dissolving sugar in water.

Even though the sugar seems to disappear, it can easily be separated back into sugar and water by evaporation.


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Changes in Matter, ContinuedC hemical C hanges involve a change in the properties of matter that change its composition.

A chemical reaction.Rusting is iron combining with oxygen to make iron(III) oxide.Burning results in butane from a lighter to be changed into carbon dioxide and water.Silver combines with sulfur in the air to make tarnish.


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Thermite

Fe2O3 + 2 Al 2 Fe + Al2O3

http://www.youtube.com/watch?v=WrCWLpRc1yMTro's "Introductory Chemistry",

Chapter 378

Is it a Physical or Chemical Change?A physical change results in a different form of the same substance.

A chemical change results in one or more completely new substances.

Also called che mical re actions.

The new substances have different molecules than the original substances.You will observe different physical properties because the new substances have their own physical properties.

http://en.wikipedia.org/wiki/Image:Thermite_mix.jpg

http://en.wikipedia.org/wiki/Image:ThermiteFe2O3.JPG

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Phase Changes ArePhysical Changes

Boiling = liquid to gas.Melting = solid to liquid.Subliming = solid to gas.Freezing = liquid to solid.Condensing = gas to liquid.Deposition = gas to solid.State changes require heating or cooling the substance.

Evaporation is not a simple phase change, it is a solution process.


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Practice Classify Each Change as Physical or Chemical

Evaporation of rubbing alcohol.Sugar turning black when heated.An egg splitting open and spilling out.Sugar fermenting.Bubbles escaping from soda.Bubbles that form when hydrogen peroxide is mixed with blood.


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Practice Classify Each Change as Physical or Chemical, Continued

Evaporation of rubbing alcohol = physical.Sugar turning black when heated = chemical.An egg splitting open and spilling out = physical.Sugar fermenting = chemical.Bubbles escaping from soda = physical.Bubbles that form when hydrogen peroxide is mixed with blood = chemical.


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Law of Conservation of MassAntoine Lavoisier

The total amount of matter present before a chemical reaction is always the same as the total amount after.The total mass of all the reactants is equal to the total mass of all the products.


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Conservation of MassTotal amount of matter remains constant in a chemical reaction.58 grams of butane burns in 208 grams of oxygen to form 176 grams of carbon dioxide and 90 grams of water.butane + oxygen carbon dioxide + water

58 grams + 208 grams 176 grams + 90 grams266 grams = 266 grams


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EnergyThere are things that do not have mass and volume.These things fall into a category we call energy.Energy is anything that has the capacity to do work.Although chemistry is the study of matter, matter is effected by energy.

It can cause physical and/or chemical changes in matter.

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Law of Conservation of Energy

The total amount of energy in the universe is constant. There is no process that can increase or decrease that amount.However, we can transfer energy from one place in the universe to another, and we can change its form.


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Matter Possesses EnergyWhen a piece of matter possesses energy, it can give some or all of it to another object.

It can do work on the other object.

All chemical and physical changes result in the matter changing energy.


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Kinds of EnergyKinetic and Potential

Pote ntial e ne rgy is energy that is stored.

Water flows because gravity pulls it downstream.

move, so it has to store that energy.Kine tic e ne rgy is energy of motion, or energy that is being transferred from one object to another.

When the water flows over the dam, some of its potential energy is converted to kinetic energy of motion.


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Some Forms of EnergyElec t rical

Kinetic energy associated with the flow of electrical charge.

H eat or The rmal Ene rgyKinetic energy associated with molecular motion.

Light or Radiant Ene rgyKinetic energy associated with energy transitions in an atom.

Nuc learPotential energy in the nucleus of atoms.

C hemicalPotential energy in the attachment of atoms or because of their position.


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Converting Forms of EnergyWhen water flows over the dam, some of its potential energy is converted to kinetic energy.

Some of the energy is stored in the water because it is at a higher elevation than the surroundings.

The movement of the water is kinetic energy.Along the way, some of that energy can be used to push a turbine to generate electricity.

Electricity is one form of kinetic energy.The electricity can then be used in your home. For example, you can use it to heat cake batter you mixed, causing it to change chemically and storing some of the energy in the new molecules that are made.


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Using EnergyWe use energy to accomplish all kinds of processes, but according to the Law of

it up!When we use energy we are changing it from one form to another.

For example, converting the chemical energy in gasoline into mechanical energy to make your car move.

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If a process was 100% efficient, we could theoretically get all the energy transformed into a useful form. Unfortunately we cannot get a 100% efficient process.

transformed into a form we cannot use.


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RideWhen you drive your car, some of the chemical potential energy stored in the gasoline is released.Most of the energy released in the combustion of gasoline is transformed into sound or heat energy that adds energy to the air rather than move your car down the road.


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Units of EnergyCalor ie (cal) is the amount of energy needed to raise one gram of water by 1 °C.

kcal = energy needed to raise 1000 g of water 1 °C.food calories = kcals.

Ene rgy Conve rsion Factors1 calorie (cal) = 4.184 joules (J)

1 food Calorie (food Cal) = 1000 calories (cal)1 kilowatt-hour (kWh) = 3.60 x 106 joules (J)


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Energy Use

Unit

Ene rgy Re quire d to Raise Te mpe rature of 1 g of Wate r by 1°C

Ene rgy Re quire d to Light 100-W Bulb for 1 Hour

Ene rgy Use d by Ave rage U.S. Citize n in 1 Day

joule (J) 4.18 3.6 x 105 9.0 x 108

calorie (cal) 1.00 8.60 x 104 2.2 x 108

Calorie (Cal) 1.00 x 10-3 86.0 2.2 x 105

kWh 1.1 x 10-6 0.100 2.50 x 102


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Chemical Potential EnergyThe amount of energy stored in a material is its chemical potential ene rgy.The stored energy arises mainly from the attachments between atoms in the molecules and the attractive forces between molecules.When materials undergo a physical change, the attractions between molecules change as their position changes, resulting in a change in the amount of chemical potential energy.When materials undergo a chemical change, the structures of the molecules change, resulting in a change in the amount of chemical potential energy. Tro's "Introductory Chemistry",

Chapter 396

Energy Changes andChemical Reactions

Chemical reactions happen most readily when energy is released during the reaction.Molecules with lots of chemical potential energy are less stable than ones with less chemical potential energy.Energy will be released when the reactants have more chemical potential energy than the products.

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Exothermic Processes

When a change results in the release of energy it is called an exothe rmic process.An exothermic chemical reaction occurs when the reactants have more chemical potential energy than the products.The excess energy is released into the surrounding materials, adding energy to them.

Often the surrounding materials get hotter from the energy released by the reaction.


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An Exothermic Reaction

Pote

ntia

l ene

rgy

Reactants

Products

Surroundings

reaction

Amount of energy released


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Endothermic Processes

When a change requires the absorption of energy it is called an endothe rmic process.An endothermic chemical reaction occurs when the products have more chemical potential energy than the reactants.The required energy is absorbed from the surrounding materials, taking energy from them.

Often the surrounding materials get colder due to the energy being removed by the reaction.


100

An Endothermic Reaction

Pote

ntia

l ene

rgy

Products

Reactants

Surroundings

reaction

Amount of energy absorbed


101

Temperature ScalesFahrenheit scale, °F.

Used in the U.S.Celsius scale, °C.

Used in all other countries.A Celsius degree is 1.8 times larger than a Fahrenheit degree.

Kelvin scale, K.Absolute scale.


102

Fahrenheit vs. CelsiusA Celsius degree is 1.8 times larger than a Fahrenheit degree.The standard used for 0° on the Fahrenheit scale is a lower temperature than the standard used for 0° on the Celsius scale.

1.832-F C

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103

The Kelvin Temperature ScaleBoth the Celsius and Fahrenheit scales have negative numbers.

Yet, real physical things are always positive amounts!The Kelvin scale is an absolute scale, meaning it measures the actual temperature of an object. 0 K is called absolute ze ro. It is too cold for matter to exist because all molecular motion would stop.

0 K = -273 °C = -459 °F.Absolute zero is a theoretical value obtained by following patterns mathematically.


104

Kelvin vs. Celsius

same as on the Celsius scale.

Kelvin scale degrees; we call them kelvins!That makes 1 K 1.8 times larger than 1 °F.

The 0 standard on the Kelvin scale is a much lower temperature than on the Celsius scale.When converting between kelvins and °C, remember that the kelvin temperature is always the larger number and always positive!

273C K


105

Energy and the Temperature of MatterThe amount the temperature of an object increases depends on the amount of heat energy added (q).

If you double the added heat energy the temperature will increase twice as much.

The amount the temperature of an object increases depending on its mass.

If you double the mass, it will take twice as much heat energy to raise the temperature the same amount.

106

Heat CapacityHeat capac i ty is the amount of heat a substance must absorb to raise its temperature by 1 °C.

cal/°C or J/°C.Metals have low heat capacities; insulators have high heat capacities.

Spec i fic heat = heat capacity of 1 gram of the substance.

cal/g°C or J/g°C.°C for liquid.

Or 1.000 cal/g°C.It is less for ice and steam.


107

Specific Heat CapacitySpec ific heat is the amount of energy required to raise the temperature of one gram of a substance by 1 °C.

energy it takes to raise its temperature a given amount.Like density, specific heat is a property of the type of matter.

It can be used to identify the type of matter.

good cooling agent.It absorbs a lot of heat for a relatively small mass.


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Specific Heat CapacitiesSubstance Specific H eat

J/g°C Aluminum 0.903

Carbon (dia) 0.508 Carbon (gra) 0.708

Copper 0.385 Gold 0.128 Iron 0.449 Lead 0.128 Silver 0.235

Ethanol 2.42 Water (l) 4.184 Water (s) 2.03 Water (g) 2.02

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109

Heat Gain or Loss by an Object

The amount of heat energy gained or lost by an object depends on 3 factors: how much material there is, what the material is, and how much the temperature changed.

Amount of He at = Mass x He at Capacity x Te mpe rature Change

q = m x C x T

chapter 1

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