Kinetics動(dòng)力學(xué)Thermodynamicsdetermineswhetherandinwhichdirectionareactionwillhappen,andwhattheconcentrationsofconstituentsareinvolvedinthereaction熱力學(xué)決定了反應(yīng)是否發(fā)生、反應(yīng)的方向以及參與到反應(yīng)之中的物質(zhì)濃度問題。Kineticssayhowfastareactionhappens,sequenceofstepsinthereaction,andsomeofthefactorsthatcontroltheratesofreactions動(dòng)力學(xué)則說明反應(yīng)發(fā)生的速率有多快、反應(yīng)步驟的順序以及控制反應(yīng)速率的一些因素FurtherReading(Chapter3inHobbs)Rateofreactionistypicallymeasuredasthechangeinconcentration(moles/L)withtime反應(yīng)速率通常通過濃度(mol/L)隨時(shí)間的變化來測(cè)量

Thischangemaybeadecreaseoranincrease改變可能是增加的也可能是減小的Likewisetheconcentrationchangemaybeofreactantsorproducts同樣，改變濃度的物質(zhì)可能是反應(yīng)物也可能是生成物反應(yīng)速率=△濃度/△時(shí)間Ratehasunitsofmolesperliterperunittime -Ms-1,Mh-1速率的單位是摩爾每升每單位時(shí)間，如Ms-1、Mh-1

Considerthehypotheticalreaction對(duì)于這個(gè)假設(shè)的反應(yīng)

aA

+bB

cC+dDWecanwriteNotetheuseofthenegativesign注意負(fù)號(hào)的使用 -rateisdefinedasapositivequantity反應(yīng)速率被定義為正量 -rateofdisappearanceofareactantis

negative那么，反應(yīng)物的消耗速率就是負(fù)的 2N2O5(g)4NO2(g)+O2(g)Ratemaybeexpressedinthreemainways:反應(yīng)速率主要有以下三個(gè)表達(dá)方式：Averagereactionrate:ameasureofthechangeinconcentrationwithtime1、平均反應(yīng)速率：濃度隨時(shí)間變化的度量2.Instantaneousrate:rateofchangeofconcentrationatanyparticularinstantduringtheReaction2、瞬時(shí)速率：反應(yīng)過程中某一特定瞬間的濃度變化速率3.Initialrate:instantaneousrateatt=0 -thatis,whenthereactantsarefirst

mixed

3、初始速率：t=0時(shí)即反應(yīng)物最初混合時(shí)的瞬時(shí)速率，RateLaws速率定律Ratelaw=amathematicalfunctiondescribingtheturnoverrateofthecompoundofinterestasafunctionoftheconcentrationsofthevariousspeciesparticipatinginthereaction速率定律：用來描述相關(guān)的化合物的轉(zhuǎn)化速率的數(shù)學(xué)函數(shù)，即各種參與反應(yīng)的物質(zhì)的濃度的函數(shù)MayormayNOThaveatheoreticalbasis可能有或沒有理論基礎(chǔ)“Manyreactionsoccuratadecreasingratewithincreasingtimebecausethereactionratediminishesastheconcentrationsofthereactantsdiminish”“很多反應(yīng)隨著時(shí)間的增加反應(yīng)速率逐漸減??？，因?yàn)榉磻?yīng)物濃度減小會(huì)降低反應(yīng)速率”Hobbs(2000)RateLaws“m”indicatestheorderofthereactionwithrespecttospecies“A”.Determinedexperimentally.“m”指關(guān)于物質(zhì)A的反應(yīng)級(jí)數(shù)，由實(shí)驗(yàn)確定?！発”=ratecoefficient

(orspecificreactionratecoeff.);determinedforaspecificreactionataspecifictemp“K”=速率常數(shù)（或特定的速率系數(shù)），由特定溫度下的具體反應(yīng)確定A===>productsReactionrateRateLaws“m,n,o”indicatetheorderofthereactionwithrespecttoeachspecies;determineexperimentallyoverallreactionorder=m+n+o“m,n,o”分別是關(guān)于每種物質(zhì)的反應(yīng)級(jí)數(shù)，實(shí)驗(yàn)確定的總反應(yīng)級(jí)數(shù)=m+n+oReactionorderscanbe:first,second,third反應(yīng)級(jí)數(shù)可以是一級(jí)、二級(jí)、三級(jí)A+B+C===>productsFirstorderreactions

一級(jí)動(dòng)力反應(yīng)Takeintegralofequationabove,andgetequationbelow:將以上等式積分，得到下面的等式：t?=0.693/kPlotoffirstorderreaction一級(jí)動(dòng)力反應(yīng)的圖片半衰期的長度固定Exampleof1storderreaction

1級(jí)動(dòng)力反應(yīng)范例Ifareactionhasasinglereactantandthevalueoftheexponentisone,thenitissaidtobeafirst-orderreaction.如果反應(yīng)物只有一種，而且指數(shù)為1，那么稱這種反應(yīng)為一級(jí)動(dòng)力反應(yīng)Writeratelawforaboveequation:H2O2(l)

H2O(l)+1/2O2(g)WikipediaSecondOrderReaction

二級(jí)動(dòng)力反應(yīng)Ifintegrated如果積分:得到1/[A]t=k”t+1/[A]oInverseconcentrationlinearintime濃度的倒數(shù)和時(shí)間程線性關(guān)系t?=1/k[Ao]Plotofsecondorderreaction2級(jí)動(dòng)力反應(yīng)圖[A]timeHalflivesarenotconstantwithtimeforsecondorderreactions二級(jí)反應(yīng)動(dòng)力學(xué)反應(yīng)物質(zhì)的半衰期隨時(shí)間推移變化Exampleof2ndorderreaction

二級(jí)動(dòng)力反應(yīng)范例Asecond-orderreactiondependsontheconcentrationsofonesecond-orderreactant,ortwofirst-orderreactants.二級(jí)動(dòng)力反應(yīng)取決是否有一個(gè)二級(jí)反應(yīng)物或者兩個(gè)一級(jí)反應(yīng)物？Writeratelawforaboveequations:2NO2(g)

2NO(g)+O2(g)WikipediaCO2+H2OH2CO3Pseudofirstorderreactions

偽一級(jí)反應(yīng)pseudo-firstorder:concentrationofonereactantremainsessentiallyconstantovertime(oftenbecauseitisinlargeexcesscomparedtotheotherreactant)偽一級(jí)動(dòng)力反應(yīng)：一種反應(yīng)物剩余的濃度基本不變（經(jīng)常由于它與其他物質(zhì)相比，濃度過量）B濃度不變ReactionMechanism反應(yīng)機(jī)理Oftenwewriteachemicalreaction我們經(jīng)常寫化學(xué)反應(yīng)式Howwewriteitisoftennothowithappens但是我們所寫的通常不是它如何發(fā)生的Manykindsofreactionmechanisms有很多反應(yīng)的機(jī)理SingleStep(Elementary)ReactionProcess

單步（基本）反應(yīng)過程Unimolecular

單分子反應(yīng)CaCO3

Ca2++CO32-Bimolecular雙分子反應(yīng)

CO2

+H2OH2CO3Termolecular

三分子反應(yīng) 2FeS2+3O2+2H2O2Fe3++4H2SO4Nofourormoremoleculeprocesseshavebeenidentifiedbecausechancesof4moleculescollidingisvery,verysmall(makingreactionratesupersmall)沒有4或者4以上的分子反應(yīng)被檢測(cè)到，因?yàn)?分子同時(shí)碰撞的機(jī)會(huì)非常非常?。ㄊ沟梅磻?yīng)速率非常?。㏑ateLawsForElementary

基本反應(yīng)速率定律Simpletowrite書寫簡(jiǎn)單UnimolecularH2CO3H++HCO3- d[H2CO3]/dt=k[H2CO3]BimolecularCO2+H2OH2CO3

d[CO2]/dt=k[CO2][H2O]Reactionorderisnotnecessarilyrelatedtothestoichiometryofthereaction,unlessthereactioniselementary.反應(yīng)級(jí)數(shù)不一定和反應(yīng)的化學(xué)計(jì)量數(shù)有關(guān)，除非反應(yīng)是基本反應(yīng)Insinglestepprocess,reactionorder=coefficientofreactantinchemicalequation在單步反應(yīng)過程中，反應(yīng)級(jí)數(shù)=化學(xué)式中反應(yīng)物的系數(shù)Complexreactionsmayormaynothavereactionordersequaltotheirstoichiometriccoefficients復(fù)雜反應(yīng)的反應(yīng)級(jí)數(shù)可能和化學(xué)計(jì)量系數(shù)相等Notallfirstorderreactions,aresinglestep,monomolecularreactions不是所有的一級(jí)反應(yīng)都是單步反應(yīng)、單分子反應(yīng)ImportantNote重要提示Hobbs(2000)OverviewofElementaryReactions

基本反應(yīng)回顧Note:forZero-Orderreactionsrateisindependentoftheconcentrationofreactant.Doublingconcentrationhasnoeffectonrate.提示：零級(jí)反應(yīng)速率不依賴反應(yīng)物的濃度，雙倍的反應(yīng)物濃度不影響反應(yīng)速率。ArrheniusEquationandTransitionStateTheory

阿倫紐斯方程和過渡態(tài)理論reactionsoccurasasequenceofelementarysteps化學(xué)反應(yīng)會(huì)發(fā)生一系列的基本步驟.usuallyoneofthesestepsismuchslowerthantheothersRateDeterminingStep通常其中的一個(gè)步驟會(huì)比其他的步驟反應(yīng)慢很多，這個(gè)就是速率決定步驟empirically,theeffectofTontherateofthisreactionstep(andthereforeontheoverallreactionrate)isdescribedbytheArrheniusequation:依照經(jīng)驗(yàn)，時(shí)間對(duì)這個(gè)步驟反應(yīng)速率（也就是整體反應(yīng)速率）的影響可以用阿倫紐斯方程描述pre-exponentialfactoror“frequencyfactor”A：指前因子或振動(dòng)因子describescollisionfrequencyandtheorientationprobability描述碰撞頻率和定向概率Activationenergy活化能（Ea是物質(zhì)分裂形成新物質(zhì)的最低能量）describesthefractionofspecieswithenergygreaterthanEa

描述了物質(zhì)能量大于Ea的部分?IncreasedTemperature=FasterReactionRates升溫=更高的反應(yīng)速率DeterminationofActivationEnergy(Ea)

活化能測(cè)定lnk2-lnk1=-Ea/R(1/T2-1/T1)K=reactionrate反應(yīng)速率Ea=activationenergy活化能R=gasconstant(8.314J/mol*K,or0.008314KJ/mol*K)氣體常數(shù)T=temperatureinKelvin開爾文溫度Example:例如kisdeterminedattwodifferenttemperaturesforthefollowingreaction:在如下反應(yīng)中，兩種不同的溫度確定了兩個(gè)k值

2HI(g)-->H2(g)+I2(g)k1=2.15x10-8Ms-1at650Kk2=2.39x10-7Ms-1at700KDeterminetheactivationenergy.Fig.13.20a,bThreeprocessescanexplainslownesstoreachequilibriumconditionsTransportDiffusionSurfaceChemicalKinetics三個(gè)過程可以解釋達(dá)到反應(yīng)平衡緩慢的原因

輸運(yùn)

擴(kuò)散

表面化學(xué)動(dòng)力學(xué)

Drever(1997)Exampleofdiffusionlimitations擴(kuò)散作用邊界Exampl