spontaneous reactions and gibb’s free energy自发反应吉布斯自由能

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1、SpontaneousReactionsandGibb’sFreeEnergyFreeEnergy–theenergygivenoffbyareactionthatisavailabletodoworkspontaneousreaction–areactionthatproceedstoformtheproductswithoutoutsideintervention·Allspontaneousreactionsreleasefreeenergyandaresaidtobeexergonic.(-G)·Whetherorn

2、otareactionisspontaneousdependsonitsentropyandenthalpy.Entropy–measureofthedisorderofasystem+Sisfavorable(S)·AllsystemsstrivetowardincreasedentropyàprefergreaterdisorderEnthalpy–heatcontentofasystem–Hisfavorable(H)·Allsystemsstrivetoreleaseenergyàprefertobeexotherm

3、icInordertodeterminethespontaneityofareactionweusetheequationforGibb’sfreeenergywhichisrelatedtoboththechangeinentropy(S)andthechangeinenthalpy(H).G=H–TSGistheGibb’sFreeEnergyHistheEnthalpyTisthetemp.inKelvinSistheEntropyIfGisnegative,thereactionisspontaneous.(Rxni

4、sexergonic.)IfGispositive,thereactionisnotspontaneous.(Rxnisendergonic.)IfGiszero,thereactionisatequilibrium.Areactionthatisnotspontaneous,thatis,areactionwitha+Gatagiventemperaturemaybecomespontaneousifthetemperatureischanged.HSGTemperature(favorable)(favorable)sp

5、ontaneousatALLtemperatures+or–spontaneousatLOWtemperatures+or–spontaneousatHIGHtemperatures(unfavorable)(unfavorable)spontaneousatNOtemperatures1.StatewhetherthevaluesforHandSwouldbepositiveornegativeandfavorableorunfavorable.UsetheseestimatestopredictwhetherGwould

6、besponataneousatalltemps,hightemps,lowtemps,ornotemps.a.2H2(g)+O2(g)à2H2O(g)+242kJExothermicreactionsoHisnegative;favorableReactantsmoredisorderedsoSisnegative;unfavorableSpontaneousatlowtemperaturesa.6CO2(g)+6H2O(l)+heatàC6H12O6(s)+6O2(g)EndothermicreactionsoHispo

7、sitive;unfavorableReactantsmoredisorderedsoSisnegative;unfavorableSpontaneousatnotemperaturesGistheGibb’sFreeEnergyHistheEnthalpyG=H–TSTisthetempinKelvinSistheEntropyHo=Ho(products)–Ho(reactants)So=So(products)–So(reactants)2.Usingthevaluesforstandardentropyandstan

8、dardenthalpy,determinewhethertheformationofCarbonDioxidegasfromthereactionofsolid.Carbon(graphite)withOxygengasisspontaneous(standardtemp=25oC)C(