chapter 6 lecture conceptual integrated science second edition © 2013 pearson education, inc. heat

Chapter 6 Lecture

ConceptualIntegrated Science

Second Edition

© 2013 Pearson Education, Inc.

Heat


This lecture will help you understand:

• The Kinetic Theory of Matter• Temperature• Absolute Zero• What Is Heat?• Quantity of Heat• The Laws of Thermodynamics• Entropy• Specific Heat Capacity• Thermal Expansion• Expansion of Water• Heat Transfer: Conduction• Heat Transfer: Convection• Heat Transfer: Radiation• Emission of Radiant Energy• Absorption of Radiant Energy


The Kinetic Theory of Matter

• Kinetic theory of matter:– Matter is made up of tiny particles (atoms or

molecules) that are always in motion.

• Thermal energy:– The total energy (kinetic and potential) of the

submicroscopic particles that make up a substance.


Temperature

Temperature– is the measure of hotness

or coldness of an object (degrees Celsius, or degrees Fahrenheit, or kelvins).

– is related to the average translational kinetic energy per molecule ina substance.


Temperature

• A thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy.

• An infrared thermometer measures temperature by the radiation a substance emits.


Temperature

• Temperature has no upper limit.• The temperature of a substance is registered

on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer.


Temperature

• Three temperature scales differ in zero point and divisions:– Celsius scale

freezing point of water: 0Cboiling point of water: 100Cdivision: 100 degree units


Temperature

• Fahrenheit scalefreezing point of water: 32Fboiling point of water: 212Fdivision: 180 degree units

• Kelvin scale (used in scientific research)freezing point of water: 273 Kboiling point of water: 373 Kdivision: same-size increments as Celsius scale


TemperatureCHECK YOUR NEIGHBOR There is twice as much molecular kinetic energy in

2 liters of boiling water as in 1 liter of boiling water.

Which is the same for both?

A. Temperature

B. Thermal energy

C. Both temperature and thermal energy

D. Neither temperature nor thermal energy

Explain your answer to your neighbor.


TemperatureCHECK YOUR ANSWERThere is twice as much molecular kinetic energy in

2 liters of boiling water as in 1 liter of boiling water.

Which is the same for both?

A. Temperature

B. Thermal energy

C. Both temperature and thermal energy

D. Neither temperature nor thermal energy

Explanation:The average kinetic energy of the molecules is the same, which means that the temperature is the same forboth.


Absolute Zero

• Absolute zero or zero K is the lowest limit of temperature at –273C where molecules have lost all available kinetic energy. A substance cannot get any colder.


What Is Heat?

• Heat is defined as a flow of thermal energy due to a temperature difference.

• The direction of heat flow is from a higher-temperature substance to a lower-temperature substance.


What Is Heat?CHECK YOUR NEIGHBOR

If a red-hot thumbtack is immersed in warm water,

the direction of heat flow will be from the

A. warm water to the red-hot thumbtack.

B. red-hot thumbtack to the warm water.

C. There is no heat flow.

D. There is not enough information.



What Is Heat?CHECK YOUR ANSWER

If a red-hot thumbtack is immersed in warm water,

the direction of heat flow will be from the

A. warm water to the red-hot thumbtack.

B. red-hot thumbtack to the warm water.

C. There is no heat flow.



Quantity of Heat

Heat is measured in units of energy—joules orcalories.

A calorie is defined as the amount of heat needed toraise the temperature of 1 gram of water by 1 Celsius degree.

4.19 joules = 1 calorie

so 4.19 joules of heat will change the temperatureof 1 gram of water by 1 Celsius degree.


Quantity of Heat

• The energy rating of food and fuel is measured by the energy released when they are metabolized.

• The heat unit for labeling food is the kilocalorie.• One kilocalorie or Calorie (with a capital C) is the

heat needed to change the temperature of1 kilogram of water by 1 degree Celsius.


Quantity of HeatCHECK YOUR NEIGHBOR

The same quantity of heat is added to different

amounts of water in two equal-size containers. The

temperature of the smaller amount of water

A. decreases more.

B. increases more.

C. does not change.




Quantity of HeatCHECK YOUR ANSWER

The same quantity of heat is added to different

amounts of water in two equal-size containers. The

temperature of the smaller amount of water

A. decreases more.

B. increases more.

C. does not change.



Quantity of HeatCHECK YOUR NEIGHBOR

You heat a half cup of tea and its temperature

rises by 4C. How much will the temperature rise if

you add the same amount of heat to a full cup of tea?

A. 0CB. 2CC. 4CD. 8C



Quantity of HeatCHECK YOUR ANSWER

You heat a half cup of tea and its temperature

rises by 4C. How much will the temperature rise if

you add the same amount of heat to a full cup of tea?

A. 0CB. 2C

C. 4CD. 8C


The Laws of Thermodynamics

• First law of thermodynamics:– Whenever heat flows into or out of a system,

the gain or loss of thermal energy equals the amount of heat transferred.

• When thermal energy transfers as heat, it does so with no net loss or gain.



• Second law of thermodynamics:– Heat never spontaneously flows from a

lower-temperature substance to a higher temperature substance.

• Heat can be made to flow the opposite wayonly when work is done on the system orwhen energy is added from another source.



• Third law of thermodynamics:– No system can reach absolute zero.


The Laws of ThermodynamicsCHECK YOUR NEIGHBORWhen work is done on a system–compressing air in a tire

pump, for example–the temperature of the system

A. increases.

B. decreases.

C. remains unchanged.

D. is no longer evident.



The Laws of ThermodynamicsCHECK YOUR ANSWERWhen work is done on a system–compressing air in a tire

pump, for example–the temperature of the system

A. increases.

B. decreases.


D. is no longer evident.

Explanation:

In accord with the first law of thermodynamics, work input

increases the energy of the system.


Entropy

• Entropy is a measure of the disorder of a system.– Whenever energy freely transforms from one form

into another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy.

Greater disorder higher entropy


Entropy

• Second law of thermodynamics — a restatement:– Natural systems tend to disperse from

concentrated and organized energy states toward diffuse and disorganized states.

• Energy tends to degrade and disperse with time.• The total amount of entropy in any system tends

to increase with time.


EntropyCHECK YOUR NEIGHBOR

Your room gets messier each week. In this case, the

entropyof your room is

A. increasing.

B. decreasing.

C. hanging steady.

D. nonexistent.



EntropyCHECK YOUR ANSWERYour room gets messier each week. In this case, theentropy of your room is

A. increasing.B. decreasing. C. hanging steady.D. nonexistent.

Comment:If your room became more organized each week, then entropywould decrease in proportion to the effort expended.


Specific Heat Capacity

• The specific heat capacity is the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius.

• Specific heat capacity is– thermal inertia that indicates the resistance of

a substance to a change in temperature.– sometimes called specific heat.


Which has a higher specific heat capacity: water or land?

A. Water

B. Land

C. Both of the above arethe same.

D. None of the above


Specific Heat CapacityCHECK YOUR NEIGHBOR


Specific Heat CapacityCHECK YOUR ANSWERWhich has a higher specific heat capacity: water or land?

A. Water

B. Land

C. Both of the above are the same.


Explanation:A substance with small temperature changes for large heatchanges has a high specific heat capacity. Water takesmuch longer to heat up in the sunshine than does land.This difference has a major influence on climate.


Thermal Expansion

• When the temperature of a substance is increased, its particles jiggle faster and move farther apart.

• All forms of matter generally expand when heated and contract when cooled.


Thermal ExpansionCHECK YOUR NEIGHBORWhen telephone lines are strung between poles in the

summer, it is advisable for the lines to

A. sag.

B. be taut.

C. be close to the ground.

D. allow ample space for birds.



Thermal ExpansionCHECK YOUR ANSWERWhen telephone lines are strung between poles in thesummer, it is advisable for the lines to

A. sag.B. be taut. C. be close to the ground.D. allow ample space for birds.

Explanation:Telephone lines are longer in a warm summer and shorter in a coldwinter. Hence, they sag more on hot summer days than during the winter.If the lines are not strung with enough sag in the summer, they mightcontract too much and snap during the winter—especially when they arecovered with ice.


Expansion of Water

• When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice less dense than water.


Expansion of Water

• Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, the water contracts until it reaches 4C. Thereafter, it expands.

• Water is at its smallest volume and greatest density at 4C. When 0C water freezes to become ice, however, it has its largest volume and lowest density.


Expansion of Water

• Volume changes for a 1-gram sample of water:


Expansion of WaterCHECK YOUR NEIGHBOR

When a sample of 0C water is heated, it first

A. expands.

B. contracts.





Expansion of WaterCHECK YOUR ANSWER

When a sample of 0C water is heated, it first

A. expands.

B. contracts.



Explanation:Water continues to contract until it reaches atemperature of 4C. With further increase intemperature beyond 4C, water then expands.


Expansion of WaterCHECK YOUR NEIGHBOR

When a sample of 4C water is cooled, it

A. expands.

B. contracts.





Expansion of WaterCHECK YOUR ANSWER

When a sample of 4C water is cooled, it

A. expands.

B. contracts.



Explanation:Parts of the water will crystallize and occupy morespace.


Heat Transfer

• Processes of thermal energy transfer:– Conduction– Convection– Radiation


Heat Transfer: Conduction

• Conduction occurs predominately in solids where the molecules remain in relatively restricted locations.



• Example:

When one end of a solid is placed near a heat source, electrons and adjacent molecules gain kinetic energy and start to move faster and farther. They collide with neighboring molecules and transfer some of their kinetic energy to them. These molecules then interact with other neighboring molecules, and thermal energy is gradually transferred along the solid.



• Good conductors– are composed of atoms with "loose" outer electrons.– are known as poor insulators.– Examples: all metals to varying degrees.

• Poor conductors– delay the transfer of heat.– are known as good insulators.– Examples: wood, wool, straw, paper, cork, Styrofoam,

liquid, gases, air or materials with trapped air



• No insulator can totally prevent heat from getting through it.

• An insulator reduces the rate at which heat penetrates.


Heat Transfer: ConductionCHECK YOUR NEIGHBORIf you hold one end of a metal bar against a piece of ice, theend in your hand will soon become cold. Does cold flow fromthe ice to your hand?

A. YesB. In some cases, yes C. NoD. In some cases, no



Heat Transfer: ConductionCHECK YOUR ANSWERIf you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand?

A. YesB. In some cases, yes C. NoD. In some cases, no

Explanation:Cold does not flow from the ice to your hand. Heat flows fromyour hand to the ice. The metal is cold to your touch becauseyou are transferring heat to the metal.


Heat Transfer: Convection

Convection– occurs in liquids and gases.– involves the movement of warmer gases or

liquids to cooler surroundings.

Two characteristics of convection:– The ability of flow—carrying thermal energy

with the fluid– The ability of warm fluid to rise in cooler

surroundings


Heat Transfer: ConvectionCHECK YOUR NEIGHBORAlthough warm air rises, why are mountaintops cold and

snow covered, while the valleys below are relatively warm

and green?

A. Warm air cools when it rises.

B. There is a thick insulating blanket of air above valleys.

C. Both of the above




Heat Transfer: ConvectionCHECK YOUR ANSWERAlthough warm air rises, why are mountaintops cold and

snow covered, while the valleys below are relatively warm

and green?

A. Warm air cools when it rises.

B. There is a thick insulating blanket of air above valleys.

C. Both of the above.

D. None of the above.

Explanation:

Earth's atmosphere acts like a blanket, which keeps Earth

from freezing at nighttime.


Heat Transfer: Radiation

• Radiation is the process by which thermal energy is transferred by electromagnetic waves.

• A thermal energy source such as the Sun converts some of its energy into electromagnetic waves. These waves carry energy, which converts back into thermal energy when absorbed by a receiver. The energy source radiates energy, and a receiver absorbs it.


Heat Transfer: Radiation

• The wavelength of radiation is related to the frequency of vibration.

Low-frequency vibrations long wavesHigh-frequency vibrations short waves


• All substances at any temperature above absolute zero emit radiant energy.

• The average frequency ( ) of radiant energy is directly proportional to the absolute temperature T of the emitter:

T

€

f

€

f

Emission of Radiant Energy


Emission of Radiant EnergyCHECK YOUR NEIGHBORIf a good absorber of radiant energy were a poor emitter, its

temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.

D. none of the above



Emission of Radiant EnergyCHECK YOUR ANSWERIf a good absorber of radiant energy were a poor emitter, its

temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.

D. none of the above

Explanation:If a good absorber were not also a good emitter, there wouldbe a net absorption of radiant energy, and the temperature of agood absorber would remain higher than the temperature ofthe surroundings. Nature is not so!


Absorption of Radiant Energy

• A material's ability to absorb and radiate thermal energy is indicated by its color.

• Good absorbers and good emitters are dark in color.

• Poor absorbers and poor emitters are reflective or light in color.



• The surface of any material both absorbs and emits radiant energy.

• When a surface absorbs more energy than it emits, it is a net absorber, and temperature rises.

• When a surface emits more energy than it absorbs, it is a net emitter, and temperature falls.



• Whether a surface is a net absorber or a net emitter depends on whether its temperature is above or below that of its surroundings.

• A surface hotter than its surroundings is a net emitter and will cool.

• A surface colder than its surroundings is a net absorber and will warm.


Absorption of Radiant EnergyCHECK YOUR NEIGHBOR

Which melts faster in sunshine: dirty snow or clean

snow?

A. Dirty snow

B. Clean snow





Absorption of Radiant EnergyCHECK YOUR ANSWER

Which melts faster in sunshine: dirty snow or clean

snow?

A. Dirty snow

B. Clean snow



Explanation:Dirty snow absorbs more sunlight, whereas cleansnow reflects more.

chapter 6 lecture conceptual integrated science second edition © 2013 pearson education, inc. heat

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