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1、16ChemicalEquilibriumReactionsseldomgocompletesuchthatoneofthereactantsisexhaustedaswehavediscussedinstoichiometryandlimitingreagent.Instead,theyaremostlyreversible.Forexample,CO(g)+3H2(g)CH4(g)+H2O(g)Thetwo-headarrow(orequalsigns=)indicatesthatthereacti
2、ongoesbothways.Similarly,N2O4(colorlessgas)2NO2(browngas)(showafilm)Whentheforwardandreversereactionratesareequal,thesystemissaidtobeatequilibrium.116ChemicalEquilibriumTheNASAComputerprogramCEA(ChemicalEquilibriumwithApplications)calculateschemicalequil
3、ibriumcompositionsandpropertiesofcomplexmixtures.Applicationsincludeassignedthermodynamicstates,theoreticalrocketperformance,Chapman-Jouguetdetonations,andshock-tubeparametersforincidentandreflectedshocks.216ChemicalEquilibrium1molCH42molS2T=1000K P=1.5at
4、mCountoursshowG/RTEquilibriumoccuratminimumG/RT316ChemicalEquilibriumASystemScientificexperimentsusuallyinvestigateasystem,whichisisolatedfromitsenvironmentorsurrounding.Thesystemcanbeanucleus,anatom,amolecule,aplant,ananimal,anexperimentalsetup,theEarth,
5、thesolarsystem,thegalaxy,ortheuniverse.Matterandenergycanbetransferredintooroutofasystem.TheenvironmentorThesurroundingTheopenorclosedsystem416ChemicalEquilibriumChemicalEquilibrium–adynamicprocessChemicalequilibriumisastateofasystemwhenreactionratesinbot
6、hdirectionsareequal.Changescontinueatthemolecularlevel,butthemacroscopicpropertiesstaythesame.Equilibriumisadynamicratherthanstaticprocess.Heatisenergyflowingfromahightemperatureobjecttoalowtemperatureobject.Equilibriumisreachedwhenthetemperaturesarethesa
7、me.Moleculesstillexchangekineticenergiesduringcollision.Waterflowsfromahighpotential-energyplacetoalowpotential-energyplace.Whenpotentialenergiesarethesame,waterstopsflowing.Water-moleculediffusioncontinues.516ChemicalEquilibriumSomeTypicalEquilibriaMacro
8、scopicpropertiessuchasvaporpressure,solubility,distributionofasubstanceintwoimmiscibleliquidsaretypicalequilibria.Vaporpressureofaliquidisthepressureofthevaporinequilibriumwithaliquid.Itisafunctionoftemperature.Solu
