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1、EXPERIMENTALDETERMINATIONOFTHEACTIVATIONENERGYOFALIGHTSTICKPurpose:Todetermine,experimentally,theactivationenergy(Ea)andfrequencyfactor(A)ofalightstickusinggraphicalanalysisBackgroundInformation:Rateconstants,asyoualreadyknow,canbeexperimentallydeterminedfromagraphobtainedbyconductingv
2、ariousreactions.Rateconstantsformostchemicalreactionscloselyfollowanequationoftheform:k=Ae-Ea/RTwhichdemonstrateshowtherateconstantdependsontemperature.ThisequationiscommonlyknownastheArrheniusequation,anditallowsustodeterminetheactivationenergyrequiredtoinitiateareactiongivenitstemper
3、ature.ThesymbolA,whichisassumedtobeaconstantforeachsubstance,isknownasthefrequencyfactor.Thefrequencyfactorisrelatedtothefrequencyofmolecularoratomiccollisionswithproperorientation(pZ)necessarytoinitiateachemicalreaction.R,thegasconstant,is8.314J/(K·mol).Logically,itmakessensethatareac
4、tion’srateconstantwoulddependontemperature,becausetemperaturewillaffecttheabilityofmoleculestocollide,interact,andreactwithpredictablefrequency.Noticethatastheactivationenergyincreasesforareaction,theexponentbecomesmorenegative,thefractionofthereactingmoleculeswithanenergygreaterthanth
5、atofEadecreases,therateconstantbecomessmaller,andtherateofthereactiondecreases.Astemperatureincreases,theexponentbecomeslessnegative,thefractionofthereactingmoleculeswithanenergygreaterthanthatofEaincreases,therateconstantbecomeslarger,andtherateofthereactionincreases.Exponentially,the
6、initialformoftheArrheniusequationisnotveryuseful.Bytakingthenaturallogarithmofbothsides,wecanarriveatthefollowing:lnk=lnAe-Ea/RTThiscanberearrangedtothefollowing:lnk=lnA+lne-Ea/RTWhich,reduced,becomes:lnk=lnA+-EaRTOr,lnk=-Ea+lnARTWhich,practically,takesthelinearformy=mx+b.Fromthis,both
7、theactivationenergy,andthefrequencyfactor,ofanynaturallyoccurringorsynthesizedreaction,maybeobtained.Thelightstickhastwoseparatechambers,onethathouseshydrogenperoxide,andonethathousesaphenyloxalateester.Whenbroken,thehydrogenperoxideoxidizesaphenyloxalateester,toformphenolandanunstab