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《Lecture 22 polymerization reactions and photochemistry reactions》由會員上傳分享，免費在線閱讀，更多相關(guān)內(nèi)容在學術(shù)論文-天天文庫。
1、Lecture22Thekineticsofcomplexreactions1Part1ChainreactionsandPolymerizationkinetics2TheratelawsofchainreactionsCH3CHO(g)CH4(g)+CO(g)overallreactionrateequationTheRice–Herzfeldmechanismforthisreactionisasfollows(thedotsignifiesanunpairedelectronandmarksaradical):
2、Initiation:CH3CHO·CH3+·CHOPropagation:CH3CHO+·CH3CH3CO·+CH4Propagation:CH3CO··CH3+COTermination:·CH3+·CH3CH3CH33Totesttheproposedmechanismweneedtoshowthatitleadstotheobservedratelaw.Accordingtothesteady-stateapproximation，thenetrateofchangeoftheintermediates(·CH
3、3andCH3CO·)maybesetequaltozero:Thesumofthetwoequationsis:Thesteady-stateconcentrationof·CH3radicalsis4ItfollowsthattherateofformationofCH4iswhichisinagreementwiththethree-halvesorderobservedexperimentallyInmanycases,achainreactionleadstoacomplicatedratelaw.Anexa
4、mpleisthehydrogen–brominereaction:5Thefollowingmechanismhasbeenproposedtoaccountforthisratelaw:Notehowthereactantsandproductsareshownasarmstothecircle,buttheintermediates(HandBr)occuronlyonthecircle.AschematicrepresentationThenetrateofformationoftheproductHBroft
5、hemechanismofthereactionbetweenhydrogenis:andbromine.6Example：Derivingtherateequationofachainreaction:Answer:Thenetratesofformationofthetwointermediatesare:7TheratelawshowsthatthereactionslowsdownasHBrforms,orasthe[HBr]/[Br2]ratioincreases.Figureshowsthatthenume
6、ricalintegrationoftheHBrratelawcanbeusedtoexplorehowtheconcentrationofHBrchangeswithtimeNumericalintegrationoftheratelawwithmathematicalsoftwareshowsthepredictedtimedependenceoftheconcentrationofHBrforthismechanism.8Self-testwhentheinitiationstepisphotolysisIabs
7、istheintensityofabsorbedradiation9Explosionsthermalexplosionchain-branchingexplosionAnexampleofbothtypesofexplosionisthereactionbetweenhydrogenandoxygen:Abranchingstepisanelementaryreactionthatproducesmorethanonechaincarrier.Forexample:Oatom:[He]2s22p4,hastwounp
8、airedelectrons.O2molecule::,with12valenceelectrons.10ThetemperatureandpressureofthesystemTheoccurrenceTheexplosionregionsforthereactionofanexplosionTheconditionsunder
