ChemicalKinetics-UMassLowell：化学动力学-麻省大学洛厄尔

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1、ChemicalKineticsTheStudyofReactionRatesChemicalKineticsKineticsinvolvesthestudyofseveralfactorsthataffecttheratesofchemicalreactions.Thefinalgoalistouseallofthedatatodevelopastep-by-stepreactionmechanism.Themechanismisapossiblepathbywhichreactantsbecomeproducts.FactorsAffe

2、ctingReactionRatesScientiststypicallyexaminehoweachofthefollowingfactorsaffecttherateofaparticularreaction.ConcentrationofReactantsTemperatureSolvent(ifapplicable)Catalysts(ifapplicable)ReactionRatesTherateofreactionistypicallyexpressedintherateofdisappearanceofreactants,o

3、rtherateofformationofproducts.Sincethestoichiometryofthereactionisknown,theconcentrationofonlyonecomponentofthereactionneedstobemeasured.ReactionRatesNotethattheconcentrationofNOincreasesbythesameamountthat[NO2]decreases.ReactionRates[O2]=½[NO]Soonlyonecomponentofthereacti

4、onneedbemeasured.ReactionRatesForthereaction:2NO2(g)2NO(g)+O2(g)rateoflossofNO2=rateofformationofNO=2(rateofformationofO2)ReactionRatesForthereaction:2NO2(g)2NO(g)+O2(g)rateoflossofNO2=rateofformationofNO=2(rateofformationofO2)-Δ[NO2]=Δ[NO]=2(Δ[O2])ΔtΔtΔtNotethenegatives

5、ignfortherateoflossofreactant.ReactionRates-Δ[NO2]=Δ[NO]=2(Δ[O2])ΔtΔtΔtThisrelationshipcanalsobeseeninagraphicalpresentationofconcentrationversustime.2NO2(g)2NO(g)+O2(g)Notethattherateofreactionvariesasthereactionproceeds.ReactionRates:2NO2(g)2NO(g)+O2(g)Therateofreactio

6、nofNO2ismostrapidatthebeginningofthereaction.Itslowsconsiderablyasthereactionproceeds.ReactionRatesReactionratesvarywithtime,andalsodependuponthetemperatureandstoichiometryofthereaction.Asaresult,wemustbeveryspecificinwhatwemeanbyareactionrate.Initialratesareoftenused.This

7、istherateofreactionjustafterthereactionbegins.Thetangenttothecurveduringtheinitialmomentsofthereactionprovidestherate.ReactionRatesThisgraphforthedecompositionofN2O5toformNO2andO2showsaninitialrateof5.4x10-4mol/L-sReactionRatesTheconventionfordealingwiththestoichiometryoft

8、hereactionisthatforageneralreaction:aA+bBcC+dDRate=-1Δ[A]=-1Δ[B]=1(Δ[C])=1(Δ[D])aΔtbΔtcΔ