課件結(jié)構(gòu)化學(xué)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反應(yīng)分子數(shù)(反應(yīng)級(jí)數(shù))Conceptofreactionorder1852-1911BerlinUniversity1901NobelPrize“inrecognitionoftheextraordinaryserviceshehasrenderedbythediscoveryofthelawsofchemicaldynamicsandosmoticpressureinsolutions”.《Studiesindynamicchemistry》~1887WilhelmOstwald1853-1932LeipzigUniversity1909NobelPrize“inrecognitionofhisworkoncatalysisandforhisinvestigationsintothefundamentalprinciplesgoverningchemicalequilibriaandratesofreaction”

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

?B/T

dependenceofrateontemperature“inrecognitionoftheextraordinaryserviceshehasrenderedtotheadvancementofchemistrybyhiselectrolytictheoryofdissociation”SvanteArrhenius1859-1927StockholmUniversityArrheniusequation12BriefHistoryofKinetics2023/4/10物理化學(xué)三劍客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

反應(yīng)速率及其單位、各表達(dá)形式間的互換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量綱:分壓·時(shí)間-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、電導(dǎo)率、電動(dòng)勢(shì)、粘度etc.)orspectroscopicmethods(IR、UV-VIS、ESR、NMR、ESCA

etc.)Techniquesformonitoringtheconcentrations物理化學(xué)實(shí)驗(yàn)九(旋光法)，十(電導(dǎo)法)2023/4/10TechniquesforrapidreactionsFlowmethodandstoppedflowtechniquesmethod(1ms-1s);Relaxationmethod(<1ms);Flashphotolysis(<1ms,-~ps).2023/4/108.3RateLawsRatelaws

速率方程Integratedratelaws

動(dòng)力學(xué)方程

Reactionorder反應(yīng)級(jí)數(shù)Ratecoefficient(rateconstant)反應(yīng)速率常數(shù)(系數(shù))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(動(dòng)力學(xué)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積分速率方程(2)Theunitofk速率常數(shù)單位(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]=?[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(馳豫時(shí)間)isalsothemeanlifetime(平均壽命）[A]=[A]0/et=1/ktiscalledtimeconstant2023/4/10一級(jí)反應(yīng)的特點(diǎn)3.速率系數(shù)k的單位為時(shí)間的負(fù)一次方，時(shí)間t可以是秒(s)，分(min)，小時(shí)(h)，天(d)和年(a)等4.半衰期(half-lifetime)t1/2

是一個(gè)與反應(yīng)物起始濃度無關(guān)的常數(shù),t1/2=ln2/k1.ln[A]與t呈線性關(guān)系，斜率為–k2.=常數(shù)=k==1

t[A]0[A]ln1

t1[A]0[A]1ln1

t2[A]0[A]2ln5.

6.

反應(yīng)間隔t相同,有定值2023/4/10Example1某金屬钚的同位素進(jìn)行β放射，14d后，同位素活性下降了6.85%。試求該同位素的：(1)蛻變常數(shù)，(2)半衰期，(3)分解掉90%所需時(shí)間。11ln1ky=-解：(1)1t2023/4/10Example2在373K，氣相反應(yīng)A→2B+C是一級(jí)反應(yīng)，從純A開始實(shí)驗(yàn)，10min時(shí)測(cè)得體系的總壓是23.47kPa，反應(yīng)終了時(shí)的總壓為36.00kPa。試由這些數(shù)據(jù)，(1)計(jì)算A的始?jí)海?2)求反應(yīng)的速率常數(shù)和半衰期，(3)計(jì)算100min時(shí)的A的壓力及總壓。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總壓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]o2023/4/10二級(jí)反應(yīng)(純二級(jí)或混二級(jí)之[A]0=[B]0)的特點(diǎn)引伸的特點(diǎn)：對(duì)的二級(jí)反應(yīng)，=1：3：7。1.與t成線性關(guān)系，斜率為k或kA(kA=ak)1[A]2.=k或kA,k的量綱為[濃度]-1

[時(shí)間]-1

1t[1[A]1[A]0]-3.半衰期與起始物濃度成反比2023/4/10二級(jí)反應(yīng)(混二級(jí)之[A]0≠[B]0)的特點(diǎn)3.半衰期只能分別對(duì)A或B定義1.ln與t成線性關(guān)系，斜率為([B]0-[A]0)k[B]/[B]0[A]/[A]02.,速率常數(shù)k的單位為

[濃度]-1

[時(shí)間]-1

2023/4/10自學(xué)(1)二級(jí)反應(yīng)aA+bB→P r=k[A][B](2)零級(jí)反應(yīng)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?jǐn)?shù)壽期(n≠1)2023/4/10n級(jí)反應(yīng)的特點(diǎn)當(dāng)n=0，2，3時(shí)，可以獲得對(duì)應(yīng)的反應(yīng)級(jí)數(shù)的積分式。但n≠1，因一級(jí)反應(yīng)有其自身的特點(diǎn)，當(dāng)n=1時(shí)，有的積分式在數(shù)學(xué)上不成立。1.與t呈線性關(guān)系1[A]n-12.=k或kA,k的量綱為[濃度]1-n[時(shí)間]-1

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

Fromintegratedratelaws—積分法(嘗試法)Isolationmethod(pseudo-reactionorder)—隔離法Methodofhalf-life—半衰期法Fromdifferentialratelaws—微分法Methodofinitialrates—初速法2023/4/10Focuses

Themostimportantthingfortheempiricalchemicalkineticsisto

establishtheratelaws

fromexperiments.Generally,thereactionorderisdeterminedinthefirststep,thentheratecoefficientisworkerout.本節(jié)要求學(xué)會(huì)，從給出的實(shí)驗(yàn)數(shù)據(jù)(濃度、分壓、物理性質(zhì)隨時(shí)間的變化；初速隨濃度的變化等)，以最簡(jiǎn)捷的方法確定反應(yīng)級(jí)數(shù)和速率常數(shù)。Focuses2023/4/10FromIntegratedRateLaws

積分法又稱嘗試法。當(dāng)實(shí)驗(yàn)測(cè)得了一系列[A]～

t或x～t的動(dòng)力學(xué)數(shù)據(jù)后，作以下兩種嘗試：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=‥*如反應(yīng)物的計(jì)量系數(shù)為n,則右邊應(yīng)除以n2023/4/10Example3t/h481216ρ/[mg?(100cm3)-1]

0.4800.3260.2220.151某抗菌素在人體血液中的分解反應(yīng)具有簡(jiǎn)單的反應(yīng)級(jí)數(shù)，給患者注射一針抗菌素后，測(cè)得抗菌素在血液中的質(zhì)量濃度ρ隨時(shí)間的變化如下表所示：(1)試求該分解反應(yīng)的級(jí)數(shù)；(2)計(jì)算反應(yīng)的速率常數(shù)和半衰期；(3)若抗菌素在人體血液中的質(zhì)量濃度不低于0.370mg?(100cm3)-1才有效，求應(yīng)該在多長(zhǎng)時(shí)間后必須注射第二針。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等時(shí)間間隔：一級(jí)反應(yīng)[A]i/[A]i+1

＝常數(shù)等時(shí)間間隔：二級(jí)反應(yīng)、零級(jí)反應(yīng)？2023/4/10MethodofHalf-lifeExpressionsofhalf-lifet1/2=ln2kIndependentofconcentrationt1/2=1k[A]0與起始濃度成反比t1/2=2k[A]02與起始濃度平方成反比3t1/2=(n-1)k[A]0n-1與起始濃度n-1次方成反比2n-1-1如反應(yīng)物的計(jì)量系數(shù)為n,則右邊應(yīng)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可將每一時(shí)間間隔起點(diǎn)的反應(yīng)物濃度作為初始濃度，根據(jù)一次的[A]~t結(jié)果確定兩組和多組t1/2~[A]0，簡(jiǎn)便判斷反應(yīng)級(jí)數(shù)。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初速法的優(yōu)點(diǎn)在于可以避免產(chǎn)物的干擾，且可適用于較慢的反應(yīng)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）該物理量對(duì)于反應(yīng)物與產(chǎn)物有明顯差異；2）與濃度有函數(shù)關(guān)系，如線性函數(shù)；3）具有加和性。2023/4/10RelationshipConsiderareaction0=∑nB·B設(shè)l0、l及l(fā)∞分別是時(shí)間為0,t及∞時(shí)體系中某物理量的值；[B]0,[B]為0及t時(shí)刻的某物種的濃度；A為某反應(yīng)物,t=∞時(shí)反應(yīng)完全，當(dāng)反應(yīng)進(jìn)度為