級物理化學(xué)-4、參考已雙語reaction kinetics

Chapter5CatalyticReaction5.1Catalystsand5.2Acid-base5.3Enzymatic5.45.55.6HeterogeneousCatalysis:SurfaceMaiReturnCatalystsandConceptsconcerningHomogeneousandheterogeneousHowacatalystMaiReturnWhatareCatalystand許多化學(xué)反應(yīng)，當(dāng)在反應(yīng)體系中加入少量反應(yīng)物種以外的其它組分()這些添加物在反應(yīng)終了時(shí)，并不進(jìn)入產(chǎn)物，而且其數(shù)量及化學(xué)性質(zhì)不因反應(yīng)而改變。這種添加物被稱為催。A+ MaiReturnHomogeneousandHeterogeneous多相催化反MaiReturnHowaCatalyst1.1.ThecatalystcannotchangetheΔrG$,equilibriumconstant(K)andmconversionoryieldcannotbeTheroleofthecatalystistoreducethetimetoreachanequilibrium。H(g)+

Δ

$＝-237kJmol- MaiReturnHowaCatalyst2Theessentialfunctionofthecatalystistodecreasetheactivationenergybychangingthereactionmechanism性介質(zhì)旁觀反應(yīng)而是反應(yīng)的積極Non-catalytic CatalyticA+B→ A+Cat.→M+B→P+ 2HO→HO+ H2O2+I－→H2O+ IO－+H2O2→H2O+O2+IMaiReturnCatalystDecreasesActivationCatalyticCatalyticAK∪ AKB[AKB]rkkkkfbEaEslowrkkkkfbMaiReturnknon-example（T=3001MaiReturnRateExpressionforaCatalyticConsiderAr=r0+If[cat.]isnotsorcat=kcat[cat][A]r0=k0[A]r=(k0+kcat[cat])[A]=kapp=k0+MaiReturnSpecialacid-baseGeneralacid-baseMaiReturnAcidandDefinitionofAcidandBr?nstedacidandbase:proton(H+)donorandacceptorLewisacidandbase:electronacceptoranddonorSpecialacidandbaseinaqueousH3O+andMaiReturnConsiderasubstrate(reactant)capableofbeingconvertedbybothnon-catalyticandacid-basecatalyzedmechanismSS+OH－→P+r=kOH－[OH－]rk0[S]kH[H][S]kOH[OHS+H+S+H+→P+r=kH+[H+]S→r=k0k0kH[H]kOH[OHMaiReturn Kappvs kapp=k0+kH+[H3O+]+kOH- ([HO+][OH-]=Klogkapp=logk0,independentofreactionslogkapp=logkH+-logkapp~pH,straightlines，slope=-log =log -- + MaiReturnMaiReturnBr?nstedAcid-catalyzedBr?nsted kapp=k0+kH+[H3O+]+ CH3COCH3＋I(xiàn)2→r=CH3COCH3→CH3C(OH)=CH2CH3C(OH)=CH2＋I(xiàn)2→CH3CI(OH)-CH2I CH3CI(OH)-CH2I→CH3COCH2I＋HI kapp=k0+kH+[H+]+MaiReturn弱酸催化的速率常數(shù)與酸離解常數(shù)不同弱酸催 碘化反應(yīng)的有關(guān)常催化（酸的離解常數(shù)(Lmol-1min-)(Lmol-鹽5.1×10-二氯乙5.1×10-α，β一二酸6.7×10-一氯乙1.5×10-乙1.8×10-

Mai

Return

Br?nstedBr?nsted關(guān)系（Br?nsted法則數(shù)常與其離解平衡常數(shù)Ka有如下關(guān)系ka=kb=MaiReturnEnzyme-catalyzedFeaturesforenzyme-catalyzedKinetics:Michaelis－MentenMaiReturnFeaturesforEnzyme-catalyzed一種酶只能催化一種或一類特定的反MaiReturnFeaturesforEnzyme-catalyzedMaiReturnMichaelis-MentenThesimplestenzymaticreactionisthatwithonlyonesubstrateandoneproduct.IthasbeenfoundthattheinitialratechangeswiththeconcentrationofthesubstratewiththefollowingcurveMaiReturnMichaelis-MentenAsimplemechanismwasproposebyMichaelisandMententoaccountthis E+ E+k-嚴(yán)格地說第二步也應(yīng)該是可故此機(jī)理只運(yùn)用于反應(yīng)初始階r k0 dt 0MaiReturnMichaelis-MentenSSapproximationforESUsingrelationship:[E]0=[E]+[ES]

d[ES]k[E][S] [ES]k[ES]d [ES]k1[Ek2k10=[E]+[ES][ES] k1[E]0(k1k2)k1[S]rk[ES] k2k1[E]0 ( k)k Michaelis-MentenMaiReturnImportantParametersinMichaelis-MentenAssumAssume:k1kMichaelisconstantMk1rm=k2[E]0MaximumrateMichaelis-Mentenequationcanbesimplifiedr rm[S]KM[S]MaiReturnMichaelis-Menten rm[S] [S]MAsr=umAs 1storderwithrespecttoAs[S]= equalstothesubstrateconcentrationM MaiReturnHowtoGetrmandrmandKMareimportantparametersforaspecificenzyme-catalyzedreactionTheycanbesimplyevaluatedfromtheLineweaver-Burkequation1r1r1KM1[S11以r

作圖，從斜率及截距可以求出MaiReturnMaiReturn其中[A]0、[B]0分別為AB初始濃度，δMaiReturn若以[B]對反應(yīng)時(shí)間t作圖可得一S型曲線，顯示有誘導(dǎo)期。反應(yīng)開始B長時(shí)間以后，A很小，反應(yīng)速率有極大值tmt=tmS的動(dòng)力學(xué)曲線上恰極點(diǎn)。由反應(yīng)動(dòng)力學(xué)曲線切線交于t軸ti，可稱此時(shí)間 自動(dòng)催化反應(yīng)的速率曲線(a)與動(dòng)力為誘導(dǎo) 曲線MaiReturn2O－+2

O+H 今在E的初始濃度為4.00×10-7moldm-3pH9.1c0/moldm-r0/moldm-3s-MaiReturnO－+

O+ O－+ O2-+ 其中E－為中間物，可視為自由基，已知k22k1,試求k1與k2(1)r0kc0根據(jù)實(shí)驗(yàn)數(shù)據(jù)得：n= k=500.72s-MaiReturn(2)根據(jù)機(jī) O－+ O+ O2－+E－ O22-+對E－d[E－]k[E][O－－k[E－][O－ [E]0=[E]+k1[E]= k1[E]=k2([E]0[E] k+ r=d[O]/dt=k

—][E]

[E]

—]=k[Ok k1+

k=2k1+

[E]0= k1=1.878×109dm3mol-1s-k=2k=3.755×109dm3mol-1s- MaiReturn總結(jié)本題雖為酶催化的題目,但并未涉及Michaelis-Menten機(jī)理,[E]0=[E]+[E－]這在Michaelis-Menten機(jī)理推導(dǎo)中也是一關(guān)鍵，MaiReturnFivetypicalstepsinheterogeneousActivesitesandMaiReturnFiveTypicalStepsinHeterogeneous發(fā)生在固體表面上的多相催化反應(yīng)可分為以下5吸附作用在多相催化中起重要MaiReturnActiveSitesandSurface固體表面上吸附反應(yīng)物的部位稱為活性部SNumberofadsorptionsitesCoverage()Numberofadsorpitonsites表面反應(yīng)速率主要決定于表面上反應(yīng)物種的覆蓋度覆蓋度與反應(yīng)物在氣~pAdsorptionisotherms吸附MaiReturnLangmuirAdsorptionThesimplestadsorptionisothermforAdsorptioncannotproceedbeyondmonolayerAllsitesareequivalentandthesurfaceisTheabilityofamoleculetoadsorbatagivensiteisindependentoftheoccupationofneighboringsitesMaiReturnLangmuirAdsorption A kap1 rd=Atequilibrium，ra= 1 ka K=kkk 1 1LangmuiradsorptionMaiReturnLangmuirAdsorption=V 1=1 1+ VmKMaiReturnLangmuirIsothermforDissociativeForadsorptionwith AkA2 S kdkap1 K1/2p1/ r=k 1K1/2p1/ Atlow =MaiReturnLangmuirIsothermforCompetitive若有i種物質(zhì)同時(shí)被同一活性位吸附，則對pi的第i組分的氣體，其覆蓋度i Ki 1 K 如A、B二種氣體 aA aB 1a a 1a a TheincreaseinpAwilldecreaseTheincreaseinpBwilldecrease這是因?yàn)锳和BMaiReturnHeterogeneousCatalysis:SurfaceUnimolecularreactions:rdnA Bimolecularreactions:rdnAk Ar k MaiReturnAssumenoAA

B r k 2 KA1KAr KA21 MaiReturnrrKA21 (1)IfpAisverylow,r=k2KApA=1stkapp=Ea=IfpAishighorKAislarge(strongadsorption),r= zerothEa=表 吸已，相力響附表.MaiReturnifaD(maybeaproductoranon-reactant)isalsoadsorbedonthecatalystsurfacer KA21 if1+KApA<<KD r

KA 速率與D的分壓成反比，即D抑制A的反MaiReturnRateofbimolecularSurfaceTherearetwomechanismsforbimolecularsurface A A(g)+B(g) S