activation energies - sd67：活化能- sd67

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1、Chemistry12Unit1–ReactionKineticsSec1.8-Activationenergies(teachernotes)PotentialandKineticenergyduringacollision+eeeeeee+eeeeeeenegativelychargedelectroncloudnegativelychargedelectroncloudRepulsiveForce-ascollidingmoleculesapproachtherepulsionslowsthemdownsoki

2、neticenergydecreases.-astheypushagainsttherepulsiveforcepotentialenergyincreases(likecompressingaspring)isconvertedto-so:KineticEnergyPotentialEnergyKE+PE=TotalE(staysconstant)ifonegoesdown,theothergoesup.PotentialEnergyDiagramsPotentialEnergy(kJ)ProgressofReac

3、tionREACTANTSPRODUCTS(HighKE,LowPE)(HighKE,LowPE)Moleculesformatemporary,unstablespeciescalledtheACTIVATEDCOMPLEXAsmoleculesapproacheachother,KEisconvertedtoPEActivatedComplexrearrangestoformthePRODUCTmoleculesProductMoleculesmoveapartandspeedup.PEisconvertedto

4、KE.Chemistry12Unit1–ReactionKineticsPotentialEnergy(kJ)REACTANTSPRODUCTSReactionProceedsThinkofthisasa“barrier”whichmustbeovercomebeforethereactioncantakeplaceACTIVATEDCOMPLEXTHEACTIVATIONENERGYBARRIERPotentialEnergy(kJ)REACTANTSPRODUCTSReactionProceedsACTIVATE

5、DCOMPLEXTHEACTIVATIONENERGYBARRIERIfcollidingmoleculesdon’thaveenoughKEtoconverttoPEtomakeit“overtheActivationEnergyBarrier”,itisanUNSUCCESSFULcollisionandthereisNOreaction.Themoleculeswilljustbounceoffofeachotherunchanged.ACTIVATIONENERGY(Ea)-Theminimumenergyr

6、equiredforasuccessfulcollision.(or)TheminimumenergyreactingmoleculesmusthaveinordertoformtheActivatedComplex.TheActivatedComplexcanbedefinedasaveryshort-lived,unstablecombinationofreactantatomsthatexistsbeforeproductsareformed.NOTE:TheActivationEnergy(Ea)isfixe

7、dbythenatureofthereactants(#’sandstrengthsofbondsinreactants.)Chemistry12Unit1–ReactionKineticsEaisNOTaffectedbyDtemperatureorDconcentration.!ProgressofReactionREACTANTSPRODUCTS102030405060708090100Ea=85-50=35kJTemperature’srole-thetemperaturedetermineshowmany(

8、orwhatfractionofthe)moleculeswillhaveenergy>Ea(tomakeitoverthebarrier&haveasuccessfulcollision)RecallKEdistributions:eg.)AtaLOWtemperature:CurveatLowerTemp.(T1)NumberofMolec