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2 a alkanes Alevel考试化学课件.pptx

发布：2024-02-16约2.97千字共27页下载文档
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Chemicalreactions

CombustionReactionwithhalogens

CombustionAlkanes,likealmostallorganiccompounds,burnwhenignitedinair.Iftheairisinexcess,theproductsarewaterandcarbondioxide.Combustionishighlyexothermicandisthemajorsourceofenergyingas-firedpowerstations:

Theequationforcompletecombustionis:Theequationforincompletecombustionis:

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Whenalkanesburninalimitedamountofair,incompletecombustiontakesplace.CO

Carbondioxideemissionscouldbereducedbyanumberofmethod,forexample:Byusingalternativesourcesofenergysuchasnuclear,windorwavepower.Byconservingenergyinthehomeandworkplace.Forexample,recyclingoldaluminiumcansrequiresmuchlessenergythanmakingnewaluminiumfrombauxiteore.

Sustainabilityandclimatechange

ThesubstitutionreactonofalkanesABCDEFGHIJ

Asubstitutionreactionisareactioninwhichoneatomorgroupisreplacedbyanotheratomorgroup.Therearealwaystworeactantsandtwoproducts.

Inthepresenceofbrightwhiteorultravioletlight,alkanesreactwithchlorineandbromine.Thereactioninvolvesthereplacementofthehydrogenatomsinthealkanebyhalogenatoms.Thereisnormallyamixtureofproductsasthehydrogenatomsaresuccessivelyreplaced.

CH4+Cl2→HCl+CH3ClCH3Cl+Cl2→HCl+CH2Cl2andsoonTheproductsarehydrogenchlorideandamixtureofchloromethane,dichloromethane,trichloromethaneandtetrachloromethane.

Thisisanexampleofafree-radicalsubstitutionreaction.Afree-radicalisanunchargedspecieswithanunpairedelectronthatisusedtoformacovalentbond.Anexampleisachlorineatom,whichhastheelectronicconfiguration.1S22S22P63S23Px23Py23Pz1

ReactionmechanismInitiationLightenergysplitsachlorinemoleculeintochlorineradicals.Cl------Cl→Cl·+Cl·UV

propagationChlorineradicalsareveryreactive.Whenachlorineradicalcollideswithamethanemoleculewithsuffici

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