chapter 16 – thermal energy and heat

Chapter 16 – Thermal Chapter 16 – Thermal Energy and HeatEnergy and Heat

Jennie L. BordersJennie L. Borders

Section 16.1 – Thermal Energy Section 16.1 – Thermal Energy and Matterand Matter

In the 1700’s most In the 1700’s most scientistsscientists thought thought that that heatheat was a was a fluidfluid called called caloriccaloric that flowed between objects.that flowed between objects.

Count RumfordCount Rumford RumfordRumford studied the process of studied the process of

drillingdrilling holes in the barrels of holes in the barrels of cannonscannons..

The process occurred in The process occurred in waterwater so that so that the the metalmetal would not would not meltmelt due to the due to the heatheat produced. produced.

RumfordRumford discovered that the discovered that the heatheat was was a result of the a result of the motionmotion of the drill, not of the drill, not a form of a form of mattermatter..

Work and HeatWork and Heat Some of the Some of the workwork done by the drill done by the drill

does useful work, but some does useful work, but some energyenergy is is lost due to lost due to frictionfriction..

HeatHeat is the transfer of is the transfer of thermal thermal energyenergy from one object to another from one object to another because of a because of a temperaturetemperature difference. difference.

HeatHeat flows spontaneously from flows spontaneously from hothot objects to objects to coldcold objects. objects.

TemperatureTemperature TemperatureTemperature is a measure of how is a measure of how hot hot

or coldor cold an object is compared to a an object is compared to a reference point.reference point.

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

As an object heats up, itsAs an object heats up, its particles move particles move fasterfaster, on, on average.average.

Thermal EnergyThermal Energy

Thermal energyThermal energy is the is the total potential total potential and kinetic energyand kinetic energy of the particles of an of the particles of an object.object.

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

Thermal energyThermal energy, unlike temperature , unlike temperature depends on depends on massmass..

Thermal ContractionThermal Contraction

Slower particlesSlower particles collide less often and collide less often and exert less force, so pressure exert less force, so pressure decreasesdecreases and the object and the object contractscontracts..

This is called This is called thermal contractionthermal contraction..

Thermal ExpansionThermal Expansion

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

Thermal expansionThermal expansion occurs when occurs when particles of matter move particles of matter move fartherfarther apart apart as temperature as temperature increasesincreases..

GasesGases expand more than expand more than liquids,liquids, and and liquidsliquids usually expand more than usually expand more than solidssolids..

Thermal ExpansionThermal Expansion

Thermal expansionThermal expansion is used in glass is used in glass thermometersthermometers..

As temperature increases, the As temperature increases, the alcohol (or mercury) in the tube alcohol (or mercury) in the tube expandsexpands and its height increases. and its height increases.

Specific HeatSpecific Heat

Specific heatSpecific heat is the amount of heat is the amount of heat needed to rise the temperature of needed to rise the temperature of one gramone gram of a material by of a material by one one degree Celsiusdegree Celsius..

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

Specific HeatSpecific Heat

Formula for Specific heat:Formula for Specific heat:

Q = m x c x Q = m x c x TT

Q = heat (J)Q = heat (J)

m = mass (g)m = mass (g)

c = specific heat (J/gc = specific heat (J/gooC)C)

T = change in temperature final – initial T = change in temperature final – initial ((ooC) C)

Sample ProblemSample Problem An iron skillet has a mass of 500.0g. The An iron skillet has a mass of 500.0g. The

specific heat of iron is 0.449 J/gspecific heat of iron is 0.449 J/gooC. How C. How much heat must be absorbed to raise the much heat must be absorbed to raise the skillet’s temperature by 95.0skillet’s temperature by 95.0ooC?C?

Q = m x c x Q = m x c x TT

m = 500.0 gm = 500.0 g

c = 0.449 J/gc = 0.449 J/gooCC

T = 95.0T = 95.0ooCC

Q =(500.0g)(0.449 J/gQ =(500.0g)(0.449 J/gooC)(95.0C)(95.0ooC) = C) = 21,327.5J21,327.5J

Practice ProblemsPractice Problems How much heat is needed to raise How much heat is needed to raise

the temperature of 100.0g of water the temperature of 100.0g of water by 85.0by 85.0ooC?C?

How much heat in kJ is absorbed by a How much heat in kJ is absorbed by a 750g iron skillet when its 750g iron skillet when its temperature rises from 25temperature rises from 25ooC to C to 125125ooC?C?

Q = (100.0g)(4.18J/goC)(85.085.0ooC) = C) = 35,530J35,530J

T = 125oC – 25oC = 100oCQ = (750g)(0.449J/goC)(100oC) = 33,675JK h d u d c m 33,675J = 33.7kJ

Practice ProblemsPractice Problems In setting up an aquarium, the heater In setting up an aquarium, the heater

transfers 1200kJ of heat to 75,000g transfers 1200kJ of heat to 75,000g of water. What is the increase in the of water. What is the increase in the water’s temperature?water’s temperature?

What mass of water will change its What mass of water will change its temperature by 3.0temperature by 3.0ooC when 525J of C when 525J of heat is added to it?heat is added to it?

Q = m x c x T T = Q/(m x c) 1200kJ = 1,200,000JT = 1,200,000J/(75,000g x 4.18J/goC) = 3.8oC

Q = m x c x T m = Q/(c x T)m = 525J/(4.18J/goC x 3.0oC) = 41.9g

CalorimeterCalorimeter

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

A A calorimetercalorimeter uses the principle that uses the principle that heat flows from a heat flows from a hotterhotter object to a object to a colder colder object until both reach the object until both reach the samesame temperature. temperature.

According to the According to the law of conservation law of conservation of energyof energy, the thermal energy , the thermal energy releasedreleased by a test sample is equal to by a test sample is equal to the thermal energy the thermal energy absorbedabsorbed by its by its surroundings.surroundings.

CalorimeterCalorimeter

Section 16.1 Section Section 16.1 Section AssessmentAssessment

In what direction does heat flow on In what direction does heat flow on its own spontaneously?its own spontaneously?

How is the temperature of an object How is the temperature of an object related to the average kinetic energy related to the average kinetic energy of its particles?of its particles?

Name two variables that affect the Name two variables that affect the thermal energy of an object.thermal energy of an object.

What causes thermal expansion of an What causes thermal expansion of an object when it is heated?object when it is heated?


How do the temperature increases of How do the temperature increases of different materials depend on their different materials depend on their specific heats?specific heats?

What principle explains how a What principle explains how a calorimeter is used to measure the calorimeter is used to measure the specific heat of a sample material?specific heat of a sample material?

Why is it necessary to have regularly Why is it necessary to have regularly spaced gaps between sections of a spaced gaps between sections of a concrete sidewalk?concrete sidewalk?


The specific heat of copper is The specific heat of copper is 0.39J/g0.39J/gooC. How much heat is needed C. How much heat is needed to raise the temperature of 1000.0g to raise the temperature of 1000.0g of copper from 25.0of copper from 25.0ooC to 45.0C to 45.0ooC?C?

A peanut burned in a calorimeter A peanut burned in a calorimeter transfers 18,200J to 100.0g of water. transfers 18,200J to 100.0g of water. What is the rise in the water’s What is the rise in the water’s temperature?temperature?

T = 45oC – 25oC = 20oCQ = (1000.0g)(0.39J/goC)(20oC) = 7800J

Q = m x c x T T = Q/(m x c) T = 18,200J/(100.0g x 4.18J/goC) = 43.5oC

Section 16.2 – Heat and Section 16.2 – Heat and ThermodynamicsThermodynamics

ConductionConduction is the transfer of thermal is the transfer of thermal energy with no overall transfer of energy with no overall transfer of mattermatter..

ConductionConduction occurs between materials occurs between materials that are that are touchingtouching..

Conduction in Conduction in gasesgases is slower than in is slower than in liquidsliquids and and solidssolids because the because the particles in a gas collide less often.particles in a gas collide less often.

ConductionConduction

In metals, In metals, conductionconduction is faster is faster because some because some electronselectrons are free to are free to move about.move about.

ConductorsConductors

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

Examples: Examples: silver, copper, gold, silver, copper, gold, aluminum, iron, steel, brass, bronze, aluminum, iron, steel, brass, bronze, mercury, graphite, dirty water, and mercury, graphite, dirty water, and concrete.concrete.

InsulatorsInsulators

A material that conducts thermal A material that conducts thermal energy poorly is called a energy poorly is called a thermal thermal insulatorinsulator..

Examples: Examples: glass, rubber, oil, asphalt, glass, rubber, oil, asphalt, fiberglass, porcelain, ceramic, quartz, fiberglass, porcelain, ceramic, quartz, cotton, paper, wood, plastic, air, cotton, paper, wood, plastic, air, diamond, and pure water.diamond, and pure water.

ConvectionConvection

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

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

ConvectionConvection

Convection currentsConvection currents are important in are important in many natural cycles, such as many natural cycles, such as ocean 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.

RadiationRadiation

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

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

ThermodynamicsThermodynamics

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

11stst Law of Thermodynamics Law of Thermodynamics

The The first law of thermodynamicsfirst law of thermodynamics states that energy is states that energy is conservedconserved..

22ndnd Law of Thermodynamics Law of Thermodynamics

The The second law of thermodynamicssecond law of thermodynamics states that thermal energy can flow states that thermal energy can flow from from coldercolder objects to objects to hotterhotter objects objects only if only if workwork is done on the system. is done on the system. ((DisorderDisorder in the universe is always in the universe is always increasingincreasing.).)

33rdrd Law of Thermodynamics Law of Thermodynamics

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


Why is conduction in gases slower Why is conduction in gases slower than conduction in liquids or solids?than conduction in liquids or solids?

Give three examples of convection Give three examples of convection currents that occur in natural cycles.currents that occur in natural cycles.

What happens to radiation from an What happens to radiation from an object as its temperature increases?object as its temperature increases?

State the first law of State the first law of thermodynamics.thermodynamics.


What is the second law of What is the second law of thermodynamics?thermodynamics?

State the third law of State the third law of thermodynamics.thermodynamics.

If you bedroom is cold, you might If you bedroom is cold, you might feel warmer with several thin feel warmer with several thin blankets than one thick one. Explain blankets than one thick one. Explain why.why.

chapter 16 – thermal energy and heat

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