课件结构化学chapter1chemical kinetics

2023/4/10PhysicalChemistry—ChemicalKineticsPhysicalChemistryBasictheoreticalsystemDisciplinarysystemThermochemistryElectrochemistryPhotochemistryCatalysisColloidandinterfacesMolecularreactiondynamicsThermodynamicsStatisticalthermodynamics(Direction&equilibriumofreactions)KineticsQuantum&structuralchemistry(Rates&mechanism)2023/4/10J.Phys.Chem.(ACS)Established1897-1997A&B2007A&B&C2010A&B&C&LettersPhysicalChemistryJournalsContentsChapter8ChemicalKineticsChapter10ChemicalKineticsforSomeSpecific

SystemsChapter9RateTheoryforElementaryReactions2023/4/102023/4/10Chapter8ChemicalKinetics8.2Ratesofreactions8.3Ratelaws8.4Integratedratelaws8.5Determinationoftheratelaw8.6Temperaturedependenceofreactionrates8.1Introductiontochemicalkinetics2023/4/10Chapter8ChemicalKinetics8.7Elementaryandcomplexreactions8.8Reactionkineticsandequilibriumstate8.10Speculationofreactionmechanism8.9Activationenergyforplexreactions2023/4/108.1IntroductiontoChemicalKineticsThelimitationsofthermodynamicsTheobjectsofchemicalkineticsBriefhistoryofchemicalkinetics2023/4/10Thermodynamics:LimitationsOndirectionsofspontaneousreaction,equilibrium,andthefactorsinfluencingtheequilibrium.Predictingpossibility

ofareaction.Forexample：Thermodynamics:can’tanswer

howtomakethemhappen;howfasttheywilltakeplace(timeasavariable);thereactionmechanism.2023/4/10ChemicalKinetics:MainObjectsThestudyofreactionrates(consideringtime),theinfluencesofvariablessuchastemperature,pressureandcatalystontherates,andthereactionmechanisms.T,P,catalystT,P,catalystChemicalKineticsChemicalKineticspossibilityreality2023/4/10MainTasksofKineticsForexamples:>700KH2+Cl2→2HClr∝[H2][Cl2]1/2H2+Br2→2HBrr∝[H2][Br2]1/2/(1+k’[HBr]/[Br2])H2+I2→2HIr∝[H2][I2]Whysodifferent？Differentreactionmechanism!1.Reactionratesandtheinfluencesofvariablesonrates2.Reactionmechanisms3.Rateofelementaryreactionsandeffectofmolecularstructures4.Natureofchemicalreactions5.Howtocontrolchemicalreactions2023/4/10Empiricalchemicalkinetics

~1864C.M.Guldberg&P.Waage(Norway)LawofMassAction

~1850LudwigF.Wilhelmy(Germany)Hydrolysisofsucrose:r=k[sucrose][H+]Therateisproportionaltotheconcentrationofthereactants

~1865Harcourt&Esson(UK)Ratelaw:differentialandintegratedformulasBriefHistoryofKinetics2023/4/10Dependenceofrateonconcentration~1884JacobusH.van’tHoffr=f(c)=k∏ciaiiai反应分子数(反应级数)Conceptofreactionorder1852-1911BerlinUniversity1901NobelPrize“inrecognitionoftheextraordinaryserviceshehasrenderedbythediscoveryofthelawsofchemicaldynamicsandosmoticpressureinsolutions”.《Studiesindynamicchemistry》~1887WilhelmOstwald1853-1932LeipzigUniversity1909NobelPrize“inrecognitionofhisworkoncatalysisandforhisinvestigationsintothefundamentalprinciplesgoverningchemicalequilibriaandratesofreaction”

BriefHistoryofKinetics2023/4/10Dependenceofrateontemperature1891SvanteA.Arrhenius1903NobelPrize1884J.H.van’tHofflnk=A

−B/T

dependenceofrateontemperature“inrecognitionoftheextraordinaryserviceshehasrenderedtotheadvancementofchemistrybyhiselectrolytictheoryofdissociation”SvanteArrhenius1859-1927StockholmUniversityArrheniusequation12BriefHistoryofKinetics2023/4/10物理化学三剑客FriedrichWilhelmOstwald1853-1932LeipzigUniversitySvanteA.Arrhenius1859-1927StockholmUniversityJacobusHendricusvan’tHoff1852-1911BerlinUniversity1901NobelPrize1903NobelPrize1909NobelPrizeBriefHistoryofKineticsvan’tHoffandOstwaldB.Harrow,“EminentChemistsofourTime”,19202023/4/102023/4/10Elementarychemicalkinetics1935Eyring:Activatedcomplextheory

(Transitionstatetheory)1913Bodenstein:Chainreactions

Semenoff&Hinshelwood:1956NobelPrize1918Lewis:Collisiontheory

RatetheoryPolanyi,WignerBriefHistoryofKinetics2023/4/10State-to-StateDynamics−MolecularReactionDynamics1960Cross-beamreactionsD.R.Herschbach-Y.T.Lee-J.C.Polanyi“fortheircontributionsconcerningthedynamicsofchemicalelementaryprocesses”(1932-)HarvardUniv.(1929-)Univ.ofToronto(1936-)UCBerkeley161986NobelPrizeBriefHistoryofKinetics2023/4/10Timescale1923H.Hartridge&F.J.W.Roughton~1950ManfredEigen10-6s1967NobelPrizeTimeResolution“fortheirstudiesofextremelyfastchemicalreactions,effectedbydisturbingtheequlibriumbymeansofveryshortpulsesofenergy”10-3sflowmethodorstoppedflowtechniques(1927-)MaxPlanckInstituteofPhysicalChemistry(Goettingen)relaxationmethodBriefHistoryofKinetics2023/4/10~1950R.G.W.Norrish&G.Porter10-6s10-9s10-12s1967NobelPrize(sharedwithM.Eigen)TimeResolution“fortheirstudiesofextremelyfastchemicalreactions,effectedbydisturbingtheequlibriumbymeansofveryshortpulsesofenergy”flashphotolysismethod(1897-1978-)InstituteofPhys.Chem.,Cambridge(1920-2002)RoyalInstitutionofGBBriefHistoryofKinetics2023/4/10~1980AhmedZewailTimeResolution1999NobelPrize“forhisstudiesofthetransitionstatesofchemicalreactionsusingfemtosecondspectroscopy”(1946-)CALTECHFemtochemistry:Atomic-ScaleDynamicsoftheChemicalBondUsingUltrafastLasers10-15sBriefHistoryofKinetics2023/4/108.2RatesofReactionsReactionratesandtheirunits

反应速率及其单位、各表达形式间的互换FocusesHowtomeasurereactionrates2023/4/10VelocityandRatevelocity

vector,withdirectionsratescalar,withoutdirection,allpositiveForexample2023/4/10ExtentofReactionConsiderareaction:aA+bB→gG+hH0=∑nBBB(nB,stoichiometricnumberofB)x=nB(t)–nB(0)nBUnit:mol2023/4/10RateofConversion&RateofReactionConsiderareaction：Rateofconversion：

mol·s-1Rateofreaction：1dnBVnBdt=mol·dm-3·s-12023/4/10RateofReactionatConstantVolumeForanyreactions：

AtconstantV：mol·dm-3·s-12023/4/10RateofReactionExpressedwithPressure

Forgaseousreactions,piseasytomeasure量纲:分压·时间-1Unit:Pa·s-1orkPa·s-1

r’=1nBdpBdtForexample：N2+3H2→2NH3r’=dpN2dt1dpH23dt=1dpNH32dt=Foridealgas,pB=cBRTr’=(RT)r2023/4/10InstantaneousRate&InitialRateInstantaneousrateistheslopeofthetangent

Inthecurveshowingthevariationofconcentrationwithtime:Initialrate:r0=-(d[R]/dt)t=0Att=0262023/4/10ReactionRateMeasurements-DrawingKineticCurvesKineticcurvesarechangesinconcentrationsofreactantsorproductswithtime.Withkineticcurves,wecangettherateofreaction.2023/4/10Techniquesformonitoringtheconcentrations(1)Chemicalmethod

Atdifferenttimes,samplingacertainamountofreactants,stoppingthereactionbycooling,dilutionandremovingcatalyst,thenmakingchemicalanalysis2023/4/10(2)Physicalmethod

Monitoringthechangesinconcentrationsusingvariousphysicalproperties(totalpressure,旋光、折射率、电导率、电动势、粘度etc.)orspectroscopicmethods(IR、UV-VIS、ESR、NMR、ESCA

etc.)Techniquesformonitoringtheconcentrations物理化学实验九(旋光法)，十(电导法)2023/4/10TechniquesforrapidreactionsFlowmethodandstoppedflowtechniquesmethod(1ms-1s);Relaxationmethod(<1ms);Flashphotolysis(<1ms,-~ps).2023/4/108.3RateLawsRatelaws

速率方程Integratedratelaws

动力学方程

Reactionorder反应级数Ratecoefficient(rateconstant)反应速率常数(系数)Focuses2023/4/10RateLaws

Inabroadsense,theratelawisanequationthatexpressestherateofreactionasafunctionofallaffectingfactors=f(c,T,catalyst,…)=Incommonsense,theratelawreferstoanequationthatexpressestherateofreactionasafunctionoftheconcentrationsofallspecies=f(c)1dcinidtmustbedeterminedfromexperiments!2023/4/10IntegratedRateLawsRatelaws=f(c)1dcinidtdifferentialequationc=f(t)IntegratedratelawsForexamples：r=-d[A]/dt=k[A]lnkt=[A]0[A]Ratelaw(速率方程)Integratedratelaws(动力学方程)2023/4/10ReactionsPossessingReactionOrdersTher=f(c)mustbedeterminedbykineticexperiments.Onlyinthiscase,reactionordersexist!aA+bB→eE+fFr=f(c)=kcAaAcBaBcEaEcFaF=k∏ciaiiFormanyreactions,2023/4/10ReactionorderThepowertowhichtheconcentrationofaspeciesisraisedistheorderwiththisspeciesTheoverallorderofareaction(n)isthesumoftheindividualordersaA,aB,aE,aFn=aA+aB+aE+aF2023/4/10Note(1)Onlywhenr=f(c)=kcAaAcBaBcEaEcFaF

=k∏ciaiReactionorderexists.(2)Reactionorderisnotthestoichiometricnumber!

Itmaybepositive,negative,integer,fractionorzero.(3)Reactionorderisdeterminedbyexperiments.Itmaybechangedwithexperimentalconditions.2023/4/10ReactionOrder:ExamplesZero-orderFirst-orderSecond-orderThird-orderNegativeFirst-order1.5-orderNosimpleorder2023/4/10Ratecoefficient

Thecoefficientintheratelawiscalledratecoefficientorrateconstant(k).(1)k

isindependentofconcentrationsofreactants.Itisgenerallyisafunctionoftemperature(ifcatalystissettled)(2)Theunitofkdependsonreactionorder(n)，

mol1-n·dm3(n-1)·s-1(3)Whenpisusedinsteadofconcentration,kp=kc(RT)1-n2023/4/10PseudoReactionOrder

Inratelaws,iftheconcentrationofonereactantisinlargeexcess,itcanbeincorporatedintothecoefficientterm,theapparentreactionordercalledpseudoreactionorder,willbedecreasedandsimplified.Forexamples:Pseudo-first-orderratelaw2023/4/108.4IntegratedRateLaws

Ratelawsaredifferentialequations,wemustintegratethemifwewanttofindtheconcentrationsasafunctionoftime.Also,theintegratedratelawsaregenerallyusedforobtainingthereactionorderandtheratelaw.2023/4/10FocusTheusuallyused

integratedratelaws积分速率方程(2)Theunitofk速率常数单位(3)half-life(t1/2)半衰期Thissectionisveryimportant,thefocusistograspthefeaturesofthereactionswithdifferentorders.FocusesForasetofexperimentaldata,howtogetnandk2023/4/10First-OrderReactionsTherateofreactionisproportionaltotheconcentrationofreactantExamples:2023/4/10First-OrderReactions:DifferentialRateLawsorConsider：DifferentialRateLaws2023/4/10First-OrderReactions:IntegratedRateLaws-ln[A]tFirst-orderreaction:-ln[A]vst–ln[A]=kt+C2023/4/10First-OrderReactions:IntegratedRateLawsln[A]0[A]=kt[A]=[A]0e(-kt)ln[A]0[A]0-x=kt=ln11-yyisthefractionofreactedA2023/4/10Half-livesFirstorderreaction:ln[A]0[A]=ktt1/2=ln2/kt3/4=2ln2/kt7/8=3ln2/kAt[A]=½[A]0t1/2

:t3/4:t7/8=1:2:3For1storderreaction:t1/2=ln2/k

t1/2

iscalledthehalf-life(半衰期)2023/4/10TimeConstantsFirstorderreaction:ln[A]0[A]=ktisalsotherelaxationtime(驰豫时间)isalsothemeanlifetime(平均寿命）[A]=[A]0/et=1/ktiscalledtimeconstant2023/4/10一级反应的特点3.速率系数k的单位为时间的负一次方，时间t可以是秒(s)，分(min)，小时(h)，天(d)和年(a)等4.半衰期(half-lifetime)t1/2

是一个与反应物起始浓度无关的常数,t1/2=ln2/k1.ln[A]与t呈线性关系，斜率为–k2.=常数=k==1

t[A]0[A]ln1

t1[A]0[A]1ln1

t2[A]0[A]2ln5.

6.

反应间隔t相同,有定值2023/4/10Example1某金属钚的同位素进行β放射，14d后，同位素活性下降了6.85%。试求该同位素的：(1)蜕变常数，(2)半衰期，(3)分解掉90%所需时间。11ln1ky=-解：(1)1t2023/4/10Example2在373K，气相反应A→2B+C是一级反应，从纯A开始实验，10min时测得体系的总压是23.47kPa，反应终了时的总压为36.00kPa。试由这些数据，(1)计算A的始压，(2)求反应的速率常数和半衰期，(3)计算100min时的A的压力及总压。解：

A→2B+Ct=t0

p000t=t

pA2(p0−pA)p0−pAt=t∞02p0

p0p∞=3p0(1)p0=p∞/3=12.00kPa(2)t=10min：pA=(3p0-pt)/2=6.265kPapt=3p0−2pA总压t

1/2=lnk/2=10.66min(3)t=100min：pA=p0e(-kt)=0.018kPa2023/4/10Second-OrderReactions2023/4/10Second-OrderReactions:IntegratedRateLaw-12AP2023/4/10Second-OrderReactions:Features-1[A]-1tSecond-orderreaction:1/[A]vstHalf-life:2023/4/10Second-OrderReactions:IntegratedRateLaw-2If[A]o=[B]oDifferentialRateLawsA+BP2023/4/10Second-OrderReactions:Features-2[A]-1tSecond-orderreaction:1/[A]vstHalf-life:2023/4/10Second-OrderReactions:IntegratedRateLaw-3If[A]o[B]o2023/4/10二级反应(纯二级或混二级之[A]0=[B]0)的特点引伸的特点：对的二级反应，=1：3：7。1.与t成线性关系，斜率为k或kA(kA=ak)1[A]2.=k或kA,k的量纲为[浓度]-1

[时间]-1

1t[1[A]1[A]0]-3.半衰期与起始物浓度成反比2023/4/10二级反应(混二级之[A]0≠[B]0)的特点3.半衰期只能分别对A或B定义1.ln与t成线性关系，斜率为([B]0-[A]0)k[B]/[B]0[A]/[A]02.,速率常数k的单位为

[浓度]-1

[时间]-1

2023/4/10自学(1)二级反应aA+bB→P r=k[A][B](2)零级反应aA→P r=kA2023/4/10nth-orderreaction:IntegratedRateLawsaA→P r=k[A]nConsider：Differentialequation(n≠1)IntegratedRateLaws2023/4/10nth-OrderReaction:Half-Lives(n≠1)2023/4/10nth-OrderReaction:分数寿期(n≠1)2023/4/10n级反应的特点当n=0，2，3时，可以获得对应的反应级数的积分式。但n≠1，因一级反应有其自身的特点，当n=1时，有的积分式在数学上不成立。1.与t呈线性关系1[A]n-12.=k或kA,k的量纲为[浓度]1-n[时间]-1

1(n-1)t[1[A]n-11[A]0n-1]-3.半衰期的表示式为：t1/2=(n-1)kA[A]0n-12n-1-12023/4/108.5DeterminationoftheRateLaw

Fromintegratedratelaws—积分法(尝试法)Isolationmethod(pseudo-reactionorder)—隔离法Methodofhalf-life—半衰期法Fromdifferentialratelaws—微分法Methodofinitialrates—初速法2023/4/10Focuses

Themostimportantthingfortheempiricalchemicalkineticsisto

establishtheratelaws

fromexperiments.Generally,thereactionorderisdeterminedinthefirststep,thentheratecoefficientisworkerout.本节要求学会，从给出的实验数据(浓度、分压、物理性质随时间的变化；初速随浓度的变化等)，以最简捷的方法确定反应级数和速率常数。Focuses2023/4/10FromIntegratedRateLaws

积分法又称尝试法。当实验测得了一系列[A]～

t或x～t的动力学数据后，作以下两种尝试：1.Putthedataof[A]~tintotheintegratedratelawsfordifferent-orderreactions,thencalculatethekIftheobtainedkisaconstant,thentheassumedreactionorderiscorrect.2.Plot,ln[A]~t,[A]-1~t,[A]-2~t

linear[A]~tzeroth-orderlinearln[A]~tfirst-orderlinear[A]-1~tsecond-order2023/4/10SummaryofIntegratedRateLawsZeroth-orderk=x

t=[A]0-[A]tFirst-orderk

=1

t[A]0[A]lnSecond-order111t[[A][A]0]-k=nth-ordera(b-x)b(a-x)1t(b-a)lnk=[A]0=[B]0

[A]0(a)≠[B]0(b)111(n-1)t[[A]n-1[A]0n-1]-k=[A]0=[B]0=‥*如反应物的计量系数为n,则右边应除以n2023/4/10Example3t/h481216ρ/[mg•(100cm3)-1]

0.4800.3260.2220.151某抗菌素在人体血液中的分解反应具有简单的反应级数，给患者注射一针抗菌素后，测得抗菌素在血液中的质量浓度ρ随时间的变化如下表所示：(1)试求该分解反应的级数；(2)计算反应的速率常数和半衰期；(3)若抗菌素在人体血液中的质量浓度不低于0.370mg•(100cm3)-1才有效，求应该在多长时间后必须注射第二针。t/h481216ρ/[mg•(100cm3)-1]

0.4800.3260.2220.151lnρ-0.734-1.121-1.505-1.8902023/4/10Example3t/h481216ρ/[mg•(100cm3)-1]

0.4800.3260.2220.151[A]i/[A]i+11.4721.4691.470等时间间隔：一级反应[A]i/[A]i+1

＝常数等时间间隔：二级反应、零级反应？2023/4/10MethodofHalf-lifeExpressionsofhalf-lifet1/2=ln2kIndependentofconcentrationt1/2=1k[A]0与起始浓度成反比t1/2=2k[A]02与起始浓度平方成反比3t1/2=(n-1)k[A]0n-1与起始浓度n-1次方成反比2n-1-1如反应物的计量系数为n,则右边应用kA(nk)First-orderSecond-ordernth-orderThird-order2023/4/10ACommonWayoftheMethodofHalf-Life

Foranth-orderreaction2.Plotlgt1/2versuslg[A]o,evaluatenfromtheslope1.Selecttwodifferentinitialconcentration[A]oand[A]o’,measurethehalf-lives.Forthesamereaction,Cisthesame,thus,lgt1/2=lgC+(1-n)lg[A]oor,2023/4/10Example42N2O5(g)→4NO2(g)+O2(g)t/min012345[N2O5]/(moldm-3)1.0000.7050.4970.3490.2460.173Determinetheorderofthereactionandcalculatetheratecoefficientandhalflife可将每一时间间隔起点的反应物浓度作为初始浓度，根据一次的[A]~t结果确定两组和多组t1/2~[A]0，简便判断反应级数。2023/4/10FromDifferentialRateLawsLargererrors,butsuitableforreactionswithnon-integerorderPlotcurveof[A]～tDrawthetangent,workout–d[A]/dtPlotln(-d[A]/dt)vs.ln[A]Procedure:

A→Pt=0

[A]0

0t=t [A] xTheslopeofthestraightlinewillbenPlotvs.ln[A]2023/4/10MethodofInitialRatelgr0=lgk+nlg[A]0Plotlgr0

versuslg[A]0,theslopeofthestraightlinewillben初速法的优点在于可以避免产物的干扰，且可适用于较慢的反应2023/4/10Example5

Theinitialrateofthereaction(A+B→P)dependedontheinitialconcentrationsofAandBasfollows:Initialconcentration/mol·dm-3cA,01.02.03.01.01.0cB,01.01.01.02.03.0r0/mol·dm-3·s-10.150.300.450.150.15Answer:Assumer=kcAmcBn

Fromthefirst3group,weknow,m=1;Fromthelast2groups,n=0;sor=kcA;k=0.15s-1.Determinetheorderofthereactionandcalculatetheratecoefficient.2023/4/10MethodofIsolationThismethodisforthesimplificationofexperiments,andmustbeusedwithothermethods1.Doexperimentat[A]>>[B]DetermineβDetermineα2.Doexperimentat[B]>>[A]2023/4/10Example:CombinationwithIsolationwithHalf-LifeMethodsForagas-phasereaction,2NO+H2→N2O+H2O,theratelawcanbeexpressedasr=kpNOapH2b,calculatea,b

andk

basedonthefollowingexperimentalresultspNOo/kPapH2o/kPat1/2/s80801.32.61.32.6808019.219.2830415Answer:Forthefirsttwogroups,pNO>>pH2,sopNOcanbeviewedunchanged,

r=kpNOoa

pH2b

=k’pH2b

Thust1/2

isforH2

Becauset1/2

isindependentofpH20,weknowb=1Fromthelattertwogroups,pH2>>pNO

r=kpH20pNOa=k”pNOa.Thust1/2

isforNOBecauset1/2

isproportionalto(pNOo)-1,wegeta=22023/4/10RelationshipofPhysicalPropertywithConcentration

Inkineticexperiments,monitoringthechangesinconcentrationsusingaphysicalproperty(l)isasimpleway,therequirementsforthephysicalpropertyare:1）该物理量对于反应物与产物有明显差异；2）与浓度有函数关系，如线性函数；3）具有加和性。2023/4/10RelationshipConsiderareaction0=∑nB·B设l0、l及l∞分别是时间为0,t及∞时体系中某物理量的值；[B]0,[B]为0及t时刻的某物种的浓度；A为某反应物,t=∞时反应完全，当反应进度为