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4.0 HEAT4.0 HEAT

4.1 THERMAL EQUILIBRIUM4.1 THERMAL EQUILIBRIUM


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Relationship between TemperatureRelationship between Temperature

and Heatand Heat

Temperature is measure of theTemperature is measure of thedegree of hotness of a bodydegree of hotness of a body

Heat is a form of energy beingHeat is a form of energy beingtransferred from a hot body to coldtransferred from a hot body to coldbodybody

The total amount of heat depends ofThe total amount of heat depends ofmass, material and temperaturemass, material and temperature


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Thedifferent betweenheatandThedifferent betweenheatand

temperaturetemperature

TemperatureTemperature

The degree ofThe degree ofhotnesshotness

Base quantityBase quantity

Unit: Kelvin (K) orUnit: Kelvin (K) ordegree Celsius (degree Celsius (OOC)C)

Measured using aMeasured using athermometerthermometer

HeatHeat

A form of energyA form of energy

Derived quantityDerived quantityUnit : Joule (J)Unit : Joule (J)


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Thermal EquilibriumThermal Equilibrium

Two body are in thermal equilibriumTwo body are in thermal equilibriumifif

(i) they are at the same temperature(i) they are at the same temperature(ii) the net rate of heat flow between(ii) the net rate of heat flow betweenthe two bodies is zerothe two bodies is zero


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ApplicationsofthermalequilibriumApplicationsofthermalequilibrium

MicrowaveMicrowave

RefrigeratorRefrigerator

ThermometerThermometer


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CalibrationofthermometerCalibrationofthermometer

The lower fixed pointThe lower fixed point

The temperature at which ice melts,The temperature at which ice melts,

i.e 0i.e 0oo

CCThe upper fixed pointThe upper fixed point

The temperature at which pureThe temperature at which purewater boils ,i.e 100water boils ,i.e 100 oo CC

Temperature O =Temperature O = lOlO ll00 x 100x 100oo CC

ll100100 ll00


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4.2 Specific HeatCapacity4.2 Specific HeatCapacity

The total amount of heat in a bodyThe total amount of heat in a bodyis affected byis affected by

(a)(a)The temperature of the bodyThe temperature of the body

(b)(b)The mass of the bodyThe mass of the body

(c)(c)The type of materialThe type of material

specific heat capacity of an objectspecific heat capacity of an object

is quantity of heat required to riseis quantity of heat required to risethe temperature of 1 kg of materialthe temperature of 1 kg of materialby 1 degree Celsiusby 1 degree Celsius


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Heat energy = mass x specific heatHeat energy = mass x specific heat

capacity xcapacity x

temperature changetemperature changeQ = mc OQ = mc O

Unit of c = J kgUnit of c = J kg --11 oo CC --11


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A material which has high specificA material which has high specific

heat capacity has properties:heat capacity has properties:

(a)(a)Takes a long time to heatedTakes a long time to heated(b)(b)Does not lose heat easilyDoes not lose heat easily

(c)(c)Usually used as a insulatorUsually used as a insulator

(d)(d)Poor heat conductorPoor heat conductor


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ApplicationsofheatcapacityApplicationsofheatcapacity

1.1. cooking utensilcooking utensilCooking utensil are made of matel whichCooking utensil are made of matel whichhas low specific heat capacity so as tohas low specific heat capacity so as toabsorb heat fasterabsorb heat faster

2. Car radiator2. Car radiatorWater is used as a coolant in the coolingWater is used as a coolant in the coolingsystem of a car engine because watersystem of a car engine because waterhas a specific heat capacityhas a specific heat capacity

3. Sea breeze3. Sea breeze4. Land breeze4. Land breeze


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4.3 Specific Latent Heat4.3 Specific Latent Heat

Latent heat is the energy transferredLatent heat is the energy transferredduring the change of the state at aduring the change of the state at aconstant temperatureconstant temperature

When a substance is heated , itsWhen a substance is heated , itsmolecules absorb heat energy and gain inmolecules absorb heat energy and gain inkinetic energykinetic energy

When melting or boiling, a substanceWhen melting or boiling, a substance

absorb latent heat, the energy is used toabsorb latent heat, the energy is used toseparate the molecules to enable theseparate the molecules to enable thechange of statechange of state


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Specific Latent HeatofFusionSpecific Latent HeatofFusion

Is the quantity of heat needed toIs the quantity of heat needed tochange 1 kg of solid to a liquid at itschange 1 kg of solid to a liquid at itsmelting point without any increase inmelting point without any increase intemperaturetemperature

Q = mlQ = ml llllll== QQ

mm

Unit = J kgUnit = J kg --11


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Specific Latent HeatofSpecific Latent Heatof

VaporisationVaporisation

Is the quantity of heat needed toIs the quantity of heat needed tochange 1 kg of liquid into gas orchange 1 kg of liquid into gas orvapour of its boiling point withoutvapour of its boiling point withoutchange in temperaturechange in temperature

Q =mlQ =mlvvllvv

== QQ

mm

Unit JkgUnit Jkg--11


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ApplicationofSpecific Latent HeatApplicationofSpecific Latent Heat

Cooling of beverageCooling of beverage

Preservation of foodPreservation of food

Steaming foodSteaming foodKilling of germs and bacteriaKilling of germs and bacteria


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4.4 GAS LAWS4.4 GAS LAWS


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BoyleslawBoyleslaw

Boyles Law state that for a fixedBoyles Law state that for a fixedmass of gas, the pressure of the gasmass of gas, the pressure of the gasP is inversly proportional to theP is inversly proportional to the

volume of the gas, V at the constantvolume of the gas, V at the constanttemperaturetemperature

pp 11

VVPV = constantPV = constant

pp11VV11 = p= p22VV22

E


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GraphGraph


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ExplanationofBoyles Law bytheExplanationofBoyles Law bythe

Kinetic TheoryKinetic Theory

At constant temperature, the averageAt constant temperature, the averagekinetic energy of the gas molecules iskinetic energy of the gas molecules isconstantconstant

When the gas is compressed, the volumeWhen the gas is compressed, the volumeis decreasedis decreased

The number of molecules per unit volumeThe number of molecules per unit volumewill increasewill increase

The rate collision of the molecules with theThe rate collision of the molecules with thewall of the container will increase, so thewall of the container will increase, so thepressure will increasepressure will increase


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CharleslawCharleslaw

State that for a fixed mass of gas,State that for a fixed mass of gas,the volume of the gas is directlythe volume of the gas is directlyproportional to the absolute temperaproportional to the absolute tempera

ture of the gas at constant pressureture of the gas at constant pressureV TV T

VV = constant= constant

TTVV11 == VV22TT11 TT22

E


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Absolute Zeroandthe Kelvin ScaleAbsolute Zeroandthe Kelvin Scale

ofTemperatureofTemperature

From the extrapolation of the VFrom the extrapolation of the V T graph of theT graph of thePP--T graph, the intersection point of the graph onT graph, the intersection point of the graph onthe temperature axis equal tothe temperature axis equal to

273273 ooCC

We defineWe define --273 oC = 0 K so that an273 oC = 0 K so that an absoluteabsolutetemperature scaletemperature scale

When matter reaches 0K or absolute zero , allWhen matter reaches 0K or absolute zero , allmolecules of the matter will have minimummolecules of the matter will have minimum

The absolute temperature scale iscalibrateThe absolute temperature scale iscalibratebased on the Celsius temperature scale, sobased on the Celsius temperature scale, sothatthat

T = + 273 KT = + 273 KU


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GraphGraph


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ExplanationofCharles LawusingExplanationofCharles Lawusing

the Kinetic Theorythe Kinetic Theory

At constant pressure, the rate of collisionAt constant pressure, the rate of collisionof the molecules with the wall of theof the molecules with the wall of thecontainer is constant.container is constant.When the gas is heated , the averageWhen the gas is heated , the averagekinetic energy of the molecules movekinetic energy of the molecules movefaster because the rate of collision per unitfaster because the rate of collision per unitarea to increasearea to increaseThe number of collision per unit areaThe number of collision per unit area

depends on the number of molecules perdepends on the number of molecules perunit volume, therefore to increase theunit volume, therefore to increase thetemperature , the volume must betemperature , the volume must beincreaseincrease


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ExplanationofPressure Law UsingExplanationofPressure Law Using

Kinetic TheoryKinetic Theory

A constant volume, the number ofA constant volume, the number ofmolecules constantmolecules constant

When the gas heated, the kineticWhen the gas heated, the kineticenergy increases, therefore theenergy increases, therefore thevelocity of the molecules increasesvelocity of the molecules increases

The number of collision per unitThe number of collision per unitsurface of gas, the pressure willsurface of gas, the pressure willincreasesincreases


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Applicationofthe Gas LawsApplicationofthe Gas Laws

Oxygen tankOxygen tank

TiresTires

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