thermochemistry or thermodynamics - texas a&m …：热化学和热力学-德克萨斯a & m…

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1、Energy&Chemistry2H2(g)+O2(g)→2H2O(g)+heatandlightThiscanbesetuptoprovideELECTRICENERGYinafuelcell.Oxidation:2H2→4H++4e-Reduction:4e-+O2+2H2O→4OH-H2/O2FuelCellEnergy,page288Energy&ChemistryENERGYisthecapacitytodoworkortransferheat.HEATistheformofenergythatflowsbetween2objectsbecauseoftheirdifferenc

2、eintemperature.Otherformsofenergy—lightelectricalkineticandpotentialPositiveandnegativeparticles(ions)attractoneanother.TwoatomscanbondAstheparticlesattracttheyhavealowerpotentialenergyNaCl—composedofNa+andCl-ions.Potential&KineticEnergyKineticenergy—energyofmotion.InternalEnergy(E)PE+KE=Internale

3、nergy(EorU)InternalEnergyofachemicalsystemdependsonnumberofparticlestypeofparticlestemperatureThehighertheTthehighertheinternalenergySo,usechangesinT(∆T)tomonitorchangesinE(∆E).ThermodynamicsThermodynamicsisthescienceofheat(energy)transfer.Heattransfersuntilthermalequilibriumisestablished.∆Tmeasur

4、esenergytransferred.SYSTEMTheobjectunderstudySURROUNDINGSEverythingoutsidethesystemDirectionalityofHeatTransferHeatalwaystransferfromhotterobjecttocoolerone.EXOthermic:heattransfersfromSYSTEMtoSURROUNDINGS.T(system)goesdownT(surr)goesupDirectionalityofHeatTransferHeatalwaystransfersfromhotterobjec

5、ttocoolerone.ENDOthermic:heattransfersfromSURROUNDINGStotheSYSTEM.T(system)goesupT(surr)goesdownEnergy&ChemistryAllofthermodynamicsdependsonthelawofCONSERVATIONOFENERGY.Thetotalenergyisunchangedinachemicalreaction.IfPEofproductsislessthanreactants,thedifferencemustbereleasedasKE.EnergyChangeinChem

6、icalProcessesPotentialEnergyofsystemdropped.Kineticenergyincreased.Therefore,youoftenfeelaTemperatureincrease.HEATCAPACITYTheheatrequiredtoraiseanobject’sTby1˚C.Whichhasthelargerheatcapacity?SpecificHeatCapacityHowmuchenergyistransferredduetoTemperaturedifference?Theheat(q)“lost”or“gained”isrelate

7、dtoa)samplemassb)changeinTandc)specificheatcapacitySpecificheatcapacity=heatlostorgainedbysubstance(J)(mass,g)(Tchange,K)TableofspecificheatcapacitiesSubstancePhasecpJg-1K-1CpJmol-1K-1Air(typicalroomconditionsA)g