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1、Chapter7ChemicalChangeThemagicofchemistrycomeswiththrillsandexcitement,flashyreactionsandfireworks,withcolourandsound.Itisnotbondingandstructurethatgrabtheimagination,butspectacleandchange.Hereisthetopicthattellstherealstoryofchemistry.Chemicalchange,morethananything,happensinacrowdedenv
2、ironment.Factorsofimportancearethestateofaggrega-tion,materialconcentration,temperatureandpressure,collectivelyknownasthermodynamicconditions.Studentsofchemistry,evenattheelementarylevel,shouldbefamiliarwiththermodynamicmodelsofchemicalreactivity.Foraconciserevisionreferto[15].Abriefsu
3、mmaryfollows.7.1ThermodynamicPotentialsThefundamentalassumptionofthermodynamicsistheconservationofen-ergy,alsoduringitsconversionfromoneformintoanother.Inchemicalapplicationsitiscumbersometoaccountfortotalenergyinallitsformsandtheproblemisavoidedbyfocussingondifferencesinenergyrathertha
4、nabsolutevalues.Asthebasisofcalculationaconvenientenergyzeroisarbi-trarilydefinedandenergy,relativetothisstate,iscalledthethermodynamicenergy,consistingofthreecomponents:XU=TS−PV+µjNj(7.1)oralternatively,∆U=q+w+tdefiningheatflux,mechanicalworkandmatterflow.TheparametersT,S,P,V,µandNreprese
5、nttemperature,entropy,pressure,volume,chemicalpotentialandmolenumber,respectively.Bydiscountingoneormoreofthese249250CHAPTER7.CHEMICALCHANGEtermsthezeropointmovestoanewlevelandalternativepotentialfunctionsaredefined,suchas:XEnthalpy:H=U+PV=TS+µjNjXFreeenergy:F=U−TS=−PV+µjNjXFreeenthalpy
6、:G=H−TS=µjNjTheseformulaeexplainthecommonterminologyforone-componentclosedsystems:H=qP,heatcontentF=wT,workfunctionG/N=µ,partialmolarfreeenthalpyThedifferentialformofthepotentialexpressionsshowsthatchemicalpoten-tialisdefinedbyafirstderivativeofeachpotential:∂U∂H∂F∂Gµ====∂N∂N∂N∂NS
7、,VS,PT,VT,PChemicalreactivity,dependingonthereactionconditions,canbedescribedequallywellintermsofanyofthesethermodynamicpotentialsandnoeffortwillbemadetodifferentiatebetweentheminthefollowingdiscussion.7.2ChemicalReactivityItispossibletogainsignificantinsightintochemicalreactivityfromaf
