Chapter 16Chapter 16Thermal Energy and Thermal Energy and

HeatHeat

16.1 Thermal 16.1 Thermal Energy and Energy and

MatterMatter

Heat is the transfer of thermal energy from one object to another because of a temperature difference.

Work and Heat

Heat flows spontaneously Heat flows spontaneously from hot objects to cold from hot objects to cold objects.objects.

Temperature

Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.

TemperatureTemperature is a measure of how is a measure of how hot or cold an object is compared to hot or cold an object is compared to a reference point. a reference point.

•On the Celsius scale, the On the Celsius scale, the reference points are the freezing reference points are the freezing and boiling points of water. and boiling points of water.

•On the Kelvin scale, On the Kelvin scale, absolute zeroabsolute zero is defined as a temperature of 0 is defined as a temperature of 0 kelvins.kelvins.

Temperature

Thermal energy is related to 2 variables:Thermal energy is the total potential and kinetic energy of all the particles in an object.

Thermal Energy

It depends on the mass, It depends on the mass, temperature, and phase temperature, and phase (solid, liquid, or gas) of an (solid, liquid, or gas) of an object. object.

Thermal expansion is an increase in the volume of a material due to a temperature increase.

Thermal Contraction and Expansion

It occurs when particles of It occurs when particles of matter move farther apart matter move farther apart as temperature increases. as temperature increases.

Specific heat is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius.

Specific Heat

The lower a material’s specific heat, The lower a material’s specific heat, the more its temperature rises when the more its temperature rises when a given amount of energy is absorbed a given amount of energy is absorbed by a given mass.by a given mass.

In this formula, heat is in In this formula, heat is in joules, mass is in grams, joules, mass is in grams, specific heat is in J/g•°C, and specific heat is in J/g•°C, and the temperature change is in the temperature change is in degrees Celsius.degrees Celsius.

Specific Heat

Calculating Specific HeatCalculating Specific Heat

An iron skillet has a An iron skillet has a mass of 500.0 grams. mass of 500.0 grams. The specific heat of iron The specific heat of iron is 0.449 J/g•°C. How is 0.449 J/g•°C. How much heat must be much heat must be absorbed to raise the absorbed to raise the skillet’s temperature by skillet’s temperature by 95.0°C?95.0°C?

Specific Heat

Calculating Specific HeatCalculating Specific Heat

Mass of iron m = 500gSpecific heat c=20449J/g∙°CChange in temp ΔT = 95 °CQ = 500 x .449 x 95Q = 21,375 J = 21.4 kJ

Specific Heat

A calorimeter is an instrument used to measure changes in thermal energy.

Specific Heat

The lower a material’s specific The lower a material’s specific heat, the more its temperature heat, the more its temperature rises when a given amount of rises when a given amount of energy is absorbed by a given energy is absorbed by a given mass. mass.

According to the According to the law of law of conservation of energyconservation of energy, the , the thermal energy released by a thermal energy released by a test sample is equal to the test sample is equal to the thermal energy absorbed by thermal energy absorbed by its surroundings. its surroundings.

The calorimeter is sealed to The calorimeter is sealed to prevent thermal energy from prevent thermal energy from escaping.escaping.

Specific Heat

A calorimeter is A calorimeter is used to measure used to measure specific heat. A specific heat. A sample is sample is heated and heated and placed in the placed in the calorimeter. The calorimeter. The temperature temperature change is change is observed. observed.

Specific Heat

Assessment Questions

1.1. What is the thermal energy of an What is the thermal energy of an object? object?

a.a. the total number of atoms or the total number of atoms or moleculesmolecules

b.b. the total kinetic energy of the atoms the total kinetic energy of the atoms or moleculesor molecules

c.c. the average kinetic energy of the the average kinetic energy of the atoms or moleculesatoms or molecules

d.d. the average mechanical energy of the average mechanical energy of the atoms or moleculesthe atoms or molecules

Assessment Questions

1.1. What is the thermal energy of an What is the thermal energy of an object? object?

a.a. the total number of atoms or the total number of atoms or moleculesmolecules

b.b. the total kinetic energy of the atoms the total kinetic energy of the atoms or moleculesor molecules

c.c. the average kinetic energy of the the average kinetic energy of the atoms or moleculesatoms or molecules

d.d. the average mechanical energy of the average mechanical energy of the atoms or moleculesthe atoms or molecules

Assessment Questions2.2. What causes a gas to expand when its What causes a gas to expand when its

temperature is increased?temperature is increased?a.a. The number of particles increases as The number of particles increases as

temperature increases.temperature increases.b.b. Each particle expands as its Each particle expands as its

temperature increases, so the total temperature increases, so the total volume increases.volume increases.

c.c. As temperature increases, more As temperature increases, more electrons leave atoms and move electrons leave atoms and move separately.separately.

d.d. As gas particles move faster, they As gas particles move faster, they overcome some forces of attraction.overcome some forces of attraction.

Assessment Questions2.2. What causes a gas to expand when its What causes a gas to expand when its

temperature is increased?temperature is increased?a.a. The number of particles increases as The number of particles increases as

temperature increases.temperature increases.b.b. Each particle expands as its Each particle expands as its

temperature increases, so the total temperature increases, so the total volume increases.volume increases.

c.c. As temperature increases, more As temperature increases, more electrons leave atoms and move electrons leave atoms and move separately.separately.

d.d. As gas particles move faster, they As gas particles move faster, they overcome some forces of attraction.overcome some forces of attraction.

Assessment Questions

3.3.The specific heat of water is The specific heat of water is 4.18 J/g•°C. How much heat is 4.18 J/g•°C. How much heat is required to raise the required to raise the temperature of 1,000 grams temperature of 1,000 grams of water by 50°C? of water by 50°C? a.a.83.6 J83.6 Jb.b.83.6 kJ83.6 kJc.c.209 J209 Jd.d.209 kJ209 kJ

Assessment Questions

3.3.The specific heat of water is The specific heat of water is 4.18 J/g•°C. How much heat is 4.18 J/g•°C. How much heat is required to raise the required to raise the temperature of 1,000 grams temperature of 1,000 grams of water by 50°C? of water by 50°C? a.a.83.6 J83.6 Jb.b.83.6 kJ83.6 kJc.c.209 J209 Jd.d.209 kJ209 kJ

Assessment Questions4.4.What property of matter can What property of matter can

be measured using a be measured using a calorimeter? calorimeter?

a.a.temperaturetemperature

b.b.thermal expansionthermal expansion

c.c.specific heatspecific heatd.d.massmass

Assessment Questions4.4.What property of matter can What property of matter can

be measured using a be measured using a calorimeter? calorimeter?

a.a.temperaturetemperature

b.b.thermal expansionthermal expansion

c.c.specific heatspecific heatd.d.massmass

Assessment Questions5.5.Temperature is the transfer of Temperature is the transfer of

thermal energy from one thermal energy from one object to another.object to another.

TrueTrueFalseFalse

Chapter 16Chapter 16Thermal Energy and Thermal Energy and

HeatHeat

16.2 Heat and 16.2 Heat and ThermodynamicsThermodynamics

Conduction

Conduction is the transfer of thermal energy with no overall transfer of matter.

Conduction in gases is Conduction in gases is slower than in liquids and slower than in liquids and solids because the particles solids because the particles in a gas collide less often.in a gas collide less often.

ConductionConduction occurs within a occurs within a material or between material or between materials that are materials that are touching. touching.

In conduction, collisions In conduction, collisions between particles transfer between particles transfer thermal energy, without thermal energy, without any overall transfer of any overall transfer of matter.matter.

Conduction

Thermal ConductorsThermal Conductors

A A thermal conductorthermal conductor is a is a material that conducts material that conducts thermal energy well.thermal energy well.

Conduction

Thermal InsulatorsThermal Insulators

A material that conducts A material that conducts thermal energy poorly is thermal energy poorly is called a called a thermal insulatorthermal insulator..

Conduction

Convection

Convection is the transfer of thermal energy when particles of a fluid move from one place to another.

Convection currents are important in Convection currents are important in many natural cycles, such as ocean many natural cycles, such as ocean currents, weather systems, and currents, weather systems, and movements of hot rock in Earth’s movements of hot rock in Earth’s interior.interior.

A A convection currentconvection current occurs occurs when a fluid circulates in a loop when a fluid circulates in a loop as it alternately heats up and as it alternately heats up and cools down. cools down.

•Air at the bottom of an oven heats Air at the bottom of an oven heats up, expands, and becomes less up, expands, and becomes less dense. The hot air rises. dense. The hot air rises.

•Rising hot air cools as it moves Rising hot air cools as it moves away from the heat source.away from the heat source.

•As a result, the coolest air is at As a result, the coolest air is at the top of the oven.the top of the oven.

Convection

Radiation

Radiation is the transfer of energy by waves moving through space.

All objects radiate energy. As All objects radiate energy. As an object’s temperature an object’s temperature increases, the rate at which increases, the rate at which it radiates energy increases. it radiates energy increases.

Heat Transfer Heat Transfer QuestionQuestion

Identify the method of heat Identify the method of heat transfer in the following: an transfer in the following: an egg cooking in a frying pan; a egg cooking in a frying pan; a warm air mass bringing a warm air mass bringing a change in weather; the wire change in weather; the wire of an electric appliance of an electric appliance becoming hot; heat from a becoming hot; heat from a fireplace warming a roomfireplace warming a room

The study of The study of conversions conversions between thermal between thermal energy and other energy and other forms of energy is forms of energy is called called thermodynamics.thermodynamics.

Thermodynamics

The first law of thermodynamics states that energy is conserved.

Thermodynamics

First Law of ThermodynamicsFirst Law of Thermodynamics

The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system.

Thermodynamics

Second Law of ThermodynamicsSecond Law of Thermodynamics

A A heat engineheat engine is any device that is any device that converts heat into work.converts heat into work.

•The efficiency of a heat engine The efficiency of a heat engine is always less than 100 is always less than 100 percent. percent.

•Thermal energy that is not Thermal energy that is not converted into work is called converted into work is called waste heat. waste heat.

•Waste heat is lost to the Waste heat is lost to the surrounding environment.surrounding environment.

Thermodynamics

Spontaneous changes will Spontaneous changes will always make a system less always make a system less orderly, unless work is done orderly, unless work is done on the system. on the system.

Thermodynamics

The third law of thermodynamics states that absolute zero cannot be reached.

Thermodynamics

Third Law of ThermodynamicsThird Law of Thermodynamics

Assessment Questions1.1. What form of energy transfer What form of energy transfer

requires the motion of requires the motion of particles of a fluid? particles of a fluid?

a.a.conductionconduction

b.b.convectionconvection

c.c.radiationradiation

d.d.insulationinsulation

Assessment Questions1.1. What form of energy transfer What form of energy transfer

requires the motion of requires the motion of particles of a fluid? particles of a fluid?

a.a.conductionconduction

b.b.convectionconvection

c.c.radiationradiation

d.d.insulationinsulation

Assessment Questions2.2. What happens in every case in What happens in every case in

which energy is added to a which energy is added to a system?system?a.a.Temperature increases.Temperature increases.b.b.Work is done on the system.Work is done on the system.c.c.All of the energy can be All of the energy can be

accounted for as work or accounted for as work or heat.heat.

d.d.An identical amount of An identical amount of energy is removed from the energy is removed from the system.system.

Assessment Questions2.2. What happens in every case in What happens in every case in

which energy is added to a which energy is added to a system?system?a.a.Temperature increases.Temperature increases.b.b.Work is done on the system.Work is done on the system.c.c.All of the energy can be All of the energy can be

accounted for as work or accounted for as work or heat.heat.

d.d.An identical amount of An identical amount of energy is removed from the energy is removed from the system.system.

Assessment Questions3.3. Thermal energy can move from a Thermal energy can move from a

cooler object to a warmer object cooler object to a warmer object when when

a.a.the warmer object is larger.the warmer object is larger.

b.b.the cooler object has more the cooler object has more thermal energy.thermal energy.

c.c. energy is transferred by energy is transferred by radiation.radiation.

d.d.work is done on the systemwork is done on the system..

Assessment Questions3.3. Thermal energy can move from a Thermal energy can move from a

cooler object to a warmer object cooler object to a warmer object when when

a.a.the warmer object is larger.the warmer object is larger.

b.b.the cooler object has more the cooler object has more thermal energy.thermal energy.

c.c. energy is transferred by energy is transferred by radiation.radiation.

d.d.work is done on the systemwork is done on the system..

Assessment Questions4.4. According to the third law of According to the third law of

thermodynamics, it is impossible thermodynamics, it is impossible a.a.to cool an object to absolute to cool an object to absolute

zero.zero.b.b.transfer thermal energy from a transfer thermal energy from a

cooler object to a warmer cooler object to a warmer object.object.

c.c. convert energy from one form to convert energy from one form to another.another.

d.d.account for all of the energy in a account for all of the energy in a system.system.

Assessment Questions4.4. According to the third law of According to the third law of

thermodynamics, it is impossible thermodynamics, it is impossible a.a.to cool an object to absolute to cool an object to absolute

zero.zero.b.b.transfer thermal energy from a transfer thermal energy from a

cooler object to a warmer cooler object to a warmer object.object.

c.c. convert energy from one form to convert energy from one form to another.another.

d.d.account for all of the energy in a account for all of the energy in a system.system.

Assessment Questions5.5.All metals are good thermal All metals are good thermal

insulators.insulators.

TrueTrueFalseFalse

Assessment Questions5.5.All metals are good thermal All metals are good thermal

insulators.insulators.

TrueTrueFalseFalse