Chapter 16Chapter 16

HeatHeat

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What is HeatWhat is Heat

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

Most objects Most objects expandexpand when exposed when exposed to heatto heat

Flows from Flows from hothot objects to objects to coldcold objectsobjects

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What is TemperatureWhat is Temperature

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

As temperature increases, the particles As temperature increases, the particles move move fasterfaster

Instrument:Instrument: THERMOMETER THERMOMETER– Measures thermal expansion Measures thermal expansion

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Thermal EnergyThermal Energy

Total potential and Total potential and Kinetic energy of Kinetic energy of all the particles in all the particles in an object. an object.

Depends on the Depends on the mass, temperature mass, temperature and phase of an and phase of an object. object.

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As temperature rises, thermal energy rises too.

Specific HeatSpecific Heat The amount of heat The amount of heat

needed to raise the needed to raise the temperature of one temperature of one gram of a material by gram of a material by one degree Celsius.one degree Celsius.

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

Measured in Joules per Measured in Joules per gram per degree gram per degree CelsiusCelsius– J/g*ºCJ/g*ºC

FormulaFormula

Q=m*c*Q=m*c*ΔΔTT Q=heat absorbed Q=heat absorbed

(unit=J)(unit=J) m=mass (unit=g)m=mass (unit=g) c=specific heatc=specific heat ΔΔT=change in T=change in

temperaturetemperature

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Heat of ______ of water

Vaporization The heat required

to boil Liquid to gas 340 J/g

Fusion The heat required

for melting Solid to liquid 2300 J/g

CalorimeterCalorimeter

An instrument used An instrument used to measure changes to measure changes in thermal energyin thermal energy

Uses the principle Uses the principle that heat flows from that heat flows from a hotter object to a a hotter object to a colder object until colder object until both reach the both reach the same temperaturesame temperature

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Kelvin ScaleKelvin Scale

Starts at 0 and Starts at 0 and goes up. (all goes up. (all positive numbers)positive numbers)

Absolute ZeroAbsolute Zero 0 0 KK No movement of No movement of

atoms or moleculesatoms or molecules Convert ºC to KConvert ºC to K

K=ºC + 273K=ºC + 273

PracticePractice

73ºC= ________ K73ºC= ________ K -50ºC= ________K-50ºC= ________K 250K= ________ºC250K= ________ºC 500K= ________ºC500K= ________ºC

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ConductionConduction The transfer of The transfer of

thermal energy with thermal energy with no overall transfer of no overall transfer of matter.matter.

Objects are Objects are touchingtouching Conduction in gases Conduction in gases

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

EX: Touching a hot EX: Touching a hot metal spoonmetal spoon

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ConvectionConvection

Transfer of thermal Transfer of thermal energy when energy when particles of a fluid particles of a fluid move from one move from one place to another.place to another.

Usually in liquids Usually in liquids and gases because and gases because they flow easythey flow easy

Ex: boiling waterEx: boiling water

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RadiationRadiation Transfer of energy Transfer of energy

by waves moving by waves moving through space.through space.

All objects radiate All objects radiate energyenergy

As an object’s As an object’s temperature temperature increases, the rate increases, the rate at which it radiates at which it radiates energy increaseenergy increase

Ex: The SunEx: The Sun

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Conductors vs. InsulatorsConductors vs. InsulatorsConductorsConductors

Materials that Materials that conducts thermal conducts thermal energy well.energy well.

Ex: Ex: – wire rack in an ovenwire rack in an oven– Pots and pansPots and pans

InsulatorsInsulators A material that A material that

conducts thermal conducts thermal energy poorly.energy poorly.

Ex:Ex:– Wooden spoonWooden spoon– AirAir

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ThermodynamicsThermodynamics

The study of The study of conversions between conversions between thermal energy and thermal energy and other forms of energyother forms of energy

Law 1Law 1– Energy is neither Energy is neither

created nor destroyed created nor destroyed

Law 2Law 2– Thermal energy can Thermal energy can

flow from colder objects flow from colder objects to hotter objects but is to hotter objects but is transfer to other itemstransfer to other items

Law 3Law 3– Absolute zero cannot be Absolute zero cannot be

reached on Earth.reached on Earth.

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