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Copyright1999,PRENTICEHALL,Chapter5,1,Thermochemistry,Chapter5,DavidP.WhiteUniversityofNorthCarolina,Wilmington,Copyright1999,PRENTICEHALL,Chapter5,2,TheNatureofEnergy,KineticandPotentialEnergyFromPhysics:Forceisapushorpullonanobject.Workistheproductofforceappliedtoanobjectoveradistance:w=FdEnergyistheworkdonetomoveanobjectagainstaforce.Kineticenergyistheenergyofmotion:,Copyright1999,PRENTICEHALL,Chapter5,3,TheNatureofEnergy,KineticandPotentialEnergyPotentialenergyistheenergyanobjectpossessesbyvirtueofitsposition.Potentialenergycanbeconvertedintokineticenergy.Example:aballofclaydroppingoffabuilding.,Copyright1999,PRENTICEHALL,Chapter5,4,TheNatureofEnergy,EnergyUnitsSIUnitforenergyisthejoule,J:Wesometimesusethecalorieinsteadofthejoule:1cal=4.184J(exactly)AnutritionalCalorie:1Cal=1000cal=1kcal,Copyright1999,PRENTICEHALL,Chapter5,5,TheNatureofEnergy,SystemsandSurroundingsSystem:partoftheuniverseweareinterestedin.Surroundings:therestoftheuniverse.,Copyright1999,PRENTICEHALL,Chapter5,6,FirstLawofThermodynamics,InternalEnergyInternalEnergy:totalenergyofasystem.Cannotmeasureabsoluteinternalenergy.Changeininternalenergy,DE=Efinal-Einitial,Copyright1999,PRENTICEHALL,Chapter5,7,RelatingDEtoHeatandWorkEnergycannotbecreatedordestroyed.Energyof(system+surroundings)isconstant.Anyenergytransferredfromasystemmustbetransferredtothesurroundings(andviceversa).Fromthefirstlawofthermodynamics:whenasystemundergoesaphysicalorchemicalchange,thechangeininternalenergyisgivenbytheheataddedtoorabsorbedbythesystemplustheworkdoneonorbythesystem:DE=q+w,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,8,RelatingDEtoHeatandWork,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,9,RelatingDEtoHeatandWork,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,10,EndothermicandExothermicProcessesEndothermic:absorbsheatfromthesurroundings.Exothermic:transfersheattothesurroundings.Anendothermicreactionfeelscold.Anexothermicreactionfeelshot.,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,11,StateFunctionsStatefunction:dependsonlyontheinitialandfinalstatesofsystem,notonhowtheinternalenergyisused.,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,12,StateFunctions,FirstLawofThermodynamics,Copyright1999,PRENTICEHALL,Chapter5,13,Enthalpy,H:Heattransferredbetweenthesystemandsurroundingscarriedoutunderconstantpressure.Canonlymeasurethechangeinenthalpy:DH=Hfinal-Hinitial=qP,Enthalpy,Copyright1999,PRENTICEHALL,Chapter5,14,ForareactionDHrxn=H(products)-H(reactants)Enthalpyisanextensiveproperty(magnitudeDHisdirectlyproportionaltoamount):CH4(g)+2O2(g)CO2(g)+2H2O(g)DH=-802kJ2CH4(g)+4O2(g)2CO2(g)+4H2O(g)DH=-1604kJWhenwereverseareaction,wechangethesignofDH:CO2(g)+2H2O(g)CH4(g)+2O2(g)DH=+802kJChangeinenthalpydependsonstate:H2O(g)H2O(l)DH=-88kJ,EnthalpiesofReaction,Copyright1999,PRENTICEHALL,Chapter5,15,HeatCapacityandSpecificHeatCalorimetry=measurementofheatflow.Calorimeter=apparatusthatmeasuresheatflow.Heatcapacity=theamountofenergyrequiredtoraisethetemperatureofanobject(byonedegree).Molarheatcapacity=heatcapacityof1molofasubstance.Specificheat=specificheatcapacity=heatcapacityof1gofasubstance.q=(specificheat)(gramsofsubstance)T.Becarefulofthesignofq.,Calorimetry,Copyright1999,PRENTICEHALL,Chapter5,16,HeatCapacityandSpecificHeat,Calorimetry,Copyright1999,PRENTICEHALL,Chapter5,17,Constant-PressureCalorimetryAtmosphericpressureisconstant!DH=qPqrxn=-qsoln=-(specificheatofsolution)(gramsofsolution)DT.,Calorimetry,Copyright1999,PRENTICEHALL,Chapter5,18,BombCalorimetry(Constant-VolumeCalorimetry)Reactioncarriedoutunderconstantvolume.Useabombcalorimeter.Usuallystudycombustion.,Calorimetry,Copyright1999,PRENTICEHALL,Chapter5,19,qrxn=-CcalorimeterT.,BombCalorimetry(Constant-VolumeCalorimetry),Calorimetry,Copyright1999,PRENTICEHALL,Chapter5,20,Hessslaw:ifareactioniscarriedoutinanumberofsteps,HfortheoverallreactionisthesumofHforeachindividualstep.Forexample:CH4(g)+2O2(g)CO2(g)+2H2O(g)H=-802kJ2H2O(g)2H2O(l)H=-88kJCH4(g)+2O2(g)CO2(g)+2H2O(l)H=-890kJ,HesssLaw,Copyright1999,PRENTICEHALL,Chapter5,21,IntheaboveenthalpydiagramnotethatH1=H2+H3,HesssLaw,Copyright1999,PRENTICEHALL,Chapter5,22,EnthalpiesofFormation,If1molofcompoundisformedfromitsconstituentelements,thentheenthalpychangeforthereactioniscalledtheenthalpyofformation,Hof.Standardconditions(standardstate):1atmand25oC(298K).Standardenthalpy,Ho,istheenthalpymeasuredwheneverythingisinitsstandardstate.Standardenthalpyofformation:1molofcompoundisformedfromsubstancesintheirstandardstates.Ifthereismorethanonestateforasubstanceunderstandardconditions,themorestableoneisused.,Copyright1999,PRENTICEHALL,Chapter5,23,EnthalpiesofFormation,Standardenthalpyofformationofthemoststableformofanelementiszero.,Copyright1999,PRENTICEHALL,Chapter5,24,Hrxn=H1+H2+H3,EnthalpiesofFormation,UsingEnthalpiesofFormationtoCalculateEnthalpiesofReactionWeuseHessLawtocalculateenthalpiesofareactionfromenthalpiesofformation.,Copyright1999,PRENTICEHALL,Chapter5,25,EnthalpiesofFormation,UsingEnthalpiesofFormationtoCalculateEnthalpiesofReactionForareaction:,Copyright1999,PRENTICEHALL,Chapter5,26,FoodsandFuels,FoodsFuelvalue=energyreleasedwhen1gofsubstanceisburned.1nutritionalCalorie,1Cal=1000cal=1kcal.Energyinourbodiescomesfromcarbohydratesandfats(mostly).Intestines:carbohydratesconvertedintoglucose:C6H12O6+6O26CO2+6H2O,DH=-2816kJFatsbreakdownasfollows:2C57H110O6+163O2114CO2+110H2O,DH=-75,520kJFats:containmoreenergy;arenotwatersoluble,soaregoodforenergystorage.,Copyright1999,PRENTICEHALL,Chapter5,27,FoodsandFuels,Foods,Copyright1999,PRENTICEHALL,Chapter5,28,FoodsandFuels,FuelsU.S.:1.0 x106kJoffuelperday.Mostfrompetroleumandnaturalgas.Remainderfromcoal,nuclear,andhydroelectric.Fossilfuelsarenotrenewable.,Copyright1999,PRENTICEHALL,Chapter5,29,FoodsandFuels,FuelsFuelvalue=energyreleasedwhen1gofsubstanceisburned.Hydrogenhasgreatpotentialasafuelwithafuelvalueof142kJ/g.,Copyright1999,PRENTICEHALL,Chapter5,30,EndofChapter5,Thermochemistry,
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