ap chemistry notes chapter 15 chemical equilibrium：ap化學筆記15章化學平衡

1、Page1FCHSWhereExcellenceisExpectedAPChemistryNotes:Chapter13ChemicalEquilibriumManyreactionsdonotruntocompletion.Butreactionconcentrationsmayceasetochange.Thesystemcontainsamixtureofreactantsproducts.Achemicalequilibrium

2、hasbeenreached.Therearephysicalequilibriaaswell:ex.constantvappressureinaclosedcontainerwithavolatileliquidsolutionsaturation.13.1TheEquilibriumConditionAchemicalequilibriumisadynamicstate.Thefwardreactionhasnotstopped.R

3、atherthereversereactionratehascaughtup.Bothratesarenowequalsooverallconcentrationsceasetochange.Fwardreaction:A?Br=kf[A]Reversereaction:B?Ar=kr[B]BeginningwithallAnoB[A]decreasesasdoesthefwardrate.[B]increasesasdoesthere

4、verserate.Eventuallytheratesbecomeequalkf[A]=kr[B].Ifwerearrangetheequationwegetkfkr=[B][A]=aconstant.TheEquilibriumConstantisaratioofproducttoreactantconcentrations.Reversibilityisindicatedbyasetofdoublearrows:AAABEx.N2

5、(g)3H2(g)A2NH3(g)13.2TheEquilibriumConstantTheequationaboveisftheHaberprocessfsynthesizingammoniafromitselements.Itisatremendouslyimptantindustrialreactionisusedtoproducethemajityofthewld’sfixednitrogen.Theprincipaluseis

6、fagriculturalfertilizersalthoughtherearelotsofothersaswell.Theinterestingthingaboutequilibriareversiblereactionsisthattheequilibriumstatecanbereachedfromeitherdirection.Wecanstartwithallreactantsallproductsamixtureofthet

7、wothesystemwillstillcometoequilibriumwithafixedvalueftheconstant.IntheHaberprocessN2(g)H2(g)aremixedatabout200atmospheres500C.Thefwardreactiondoesnotgotocompletion.Againequilibriumcanbereachedfromeitherdirection.Seethedi

8、agramsbelow:H2NH3N2PtimeEquilibriumachievedBychangingthestartingconcentrationsexaminingtheconcentrationsatequilibriumwecanlearnmeabouttheequilibriumsystem.Page3FCHSWhereExcellenceisExpectedThesymbolslooklikethis:PNH3wher

9、ePstsfpressure(usuallyinatomospheres)thesubisfthegasinquestion.InthespacebelowwritetheequilibriumexpressionsftheaboveHaberprocessintermsofpressureusingKpinsteadofKc.?ItispossibletorelateKctoKpthroughasimpleequation:Kp=Kc

10、(RT)?n?where?nisthechangeinthenumberofmolesofgas:totalmolesproductgasestotalmolesreactantgases?TisKelvintemp.?Ristheuniversalgasconstantintheappropriateunits.13.4HeterogeneousEquilibriaInhomogeneousequilibrialiketheexamp

11、leswehaveseensofarallreactantsproductsareinthesamephase.Inheterogeneousequilibriathematerialsarenotallinthesamephase.Asitturnsoutonlygasesdissolvedmaterialsarereallysubjecttoanyappreciableconcentrationchangeasreactionsoc

12、cur.Solidsliquidsbycomparisonhaveconcentrationsthataresohighthattheyareessentiallyconstant.Therefesolidsliquidsareleftoutofequilibriumconstantexpressions.Eithertheyarepresentinwhichcaseequilibriumcanbereachedtheyarenot.E

13、x.CaCO3(s)ACaO(s)CO2(g)Kc=[CO2]Kp=PCO213.5ApplicationsofEquilibriumConstantsKnowingtheequilibriumconstantfasystemgivesthechemistvaluableinfmationaboutseveralthings:1.thetendencyfthereactiontooccuratall(butnothowfastitmay

14、occur)2.howmuchproductwillfmatagiventemperature3.whetheragivensetofconcentrationswillseethesystematequilibriumnot.Pp.5912inyourtexthavesomerepresentativepicturesofhowanequilibriumconstantiscalculated.TheExtentofaReaction

15、IfthenumericalvalueofKissmall(1)theproductsarefaved.Ex.productionofphosgene:CO(g)Cl2(g)ACOCl2(g)Kc=4.57x109Ex.N2(g)O2(g)A2NO(g)Kc=1x1030Kmustbecalculatedusingexperimentalvaluesfconcentrations.AlsoifKisknownequilibrium[]’

16、scanbecalculatedifjustonevalueisknown.Thisisamajtypeofproblemfthisunittheygetreallyfun!!SometimeswedonotknowalloftheconcentrationsofproductsreactantsatequilibriumsoifweknowinitialconcentrationsKwecancalculatetheothers.To