1GDR,1950

Sweden,1980

PostalstampsmemorizingNernst'sscientificachievements

2In1887NernstjoinedWilhelmOstwaldatLeipzigUniversity,wherevan'tHoffandArrheniuswerealreadyestablished,anditwasinthisdistinguishedcompanyofphysicalchemiststhatNernstbeganhisimportantresearches.Nernst'searlystudiesinelectrochemistrywereinspiredbyArrhenius'dissociationtheorywhichfirstrecognizedtheimportanceofionsinsolution.

In1889,heshowedhowthecharacteristicsofthecurrentproducedcouldbeusedtocalculatethefreeenergychangeinthechemicalreactionproducingthecurrent.Nernstfirstexplainedtheionizationofcertainsubstanceswhendissolvedinwater.Heconstructedanequation,knownastheNernstEquation,whichrelatedthevoltageofacelltoitsproperties.IndependentlyofThomson,heexplainedwhycompoundsionizeeasilyinwater.Theexplanation,calledtheNernst-Thomsonrule,holdsthatitisdifficultforchargedionstoattracteachotherthroughinsulatingwatermolecules,sotheydissociate.

3GrazUniversity,1887

(Standing,fromtheleft)WaltherNernst,FranzStreintz,SvanteArrhenius,Hiecke,(sitting,fromtheleft)Aulinger,AlbertvonEttingshausen,LudwigBoltzmann,IgnazKlemencic,V.Hausmanninger.4Chapter7ChemicalKinetics——RateofReaction化學動力學發(fā)展的三個階段：1.十九世紀后半葉：宏觀化學動力學階段1863年，挪威化學家古德貝格和瓦格，質(zhì)量作用定律；1889年,阿累尼烏斯定律；2.1900~1950，——碰撞理論、過渡態(tài)理論；鏈反應（自由基，用NMR法）3.1950年以后，微觀化學動力學(microscopicchemicalkinetics)/分子反應動態(tài)學(molecularreactiondynamics)：在分子水平來研究分子的一次碰撞行為中的變化，基元反應的微觀歷程.5Aimstodiscussthreeissues:1Definitionsofreactionrate2Factorsaffectingtherateofareaction2-1Concentration2-2Temperatures2-3Reactantstate(反應物之間接觸情況)2-4Catalysts3TheoryofReactionRates3-1CollisionTheory3-2ActivatedComplexTheory

6Definitionsofreactionrate

（1）AverageratesDefinition1:r=?C/?t>0,unit：mol·L-1·s-1Forexample:N2+3H2=2NH3t=0(mol·L-1)1.03.00t=2s(mol·L-1)0.82.40.4rN2=-(0.8-1.0)/2=0.1(mol·L-1·s-1)rH2=-(2.4-3.0)/2=0.3(mol·L-1·s-1)rNH3=0.4/2=0.2(mol·L-1·s-1)Thatis,rN2

：

rH2

：rNH3=1：3：2rN2/1=

rH2/3=rNH3/27ForareactionaA+bB

gG+hH

Def.2r=?C/(Vi

?t)8(2)Instantaneousrates(瞬時速率)

r=lim?C/?tr=lim?C/(Vi

?t)

?t

0?t

0

2N2O5=2N2O4+O2瞬時速率是濃度隨時間的變化率。9Example7-1At40.00

Cincarbontetrachloride,dinitrogenpentoxideisdecomposedtooxygenaccordingtothefollowingequation:2N2O5=2N2O4+O2.AccordingtothedatausedtoplotFigure7-1A,1.15mLofSTPoxygengaswereformedinthefirst300s,

7.42mLofSTPoxygengaswereformedinthefirst3000s.(1)WhatistheaveragerateofformationofSTPoxygengasduringthefirst300s?WhatistheaveragerateofformationofSTPoxygengasduringthefirst3000s?(2)WhatistheinitialrateofformationofSTPoxygen?Figure7-1A10Example7-1At40.00

Cincarbontetrachloride,dinitrogenpentoxideisdecomposedtooxygenaccordingtothefollowingequation:2N2O5=2N2O4+O2.AccordingtothedatausedtoplotFigure7-1A,1.15mLofSTPoxygengaswereformedinthefirst300s,7.42mLofSTPoxygengaswereformedinthefirst3000s.(1)WhatistheaveragerateofformationofSTPoxygengasduringthefirst300s?WhatistheaveragerateofformationofSTPoxygengasduringthefirst3000s?(2)WhatistheinitialrateofformationofSTPoxygen?SOLUTIONAveragerateofformationofoxygen=1.15mL/300s=0.00383mL/s=3.83

10-3mL/sAveragerateofformationofoxygen=7.42/3000=2.47

10-3(mL/s)(2)slopeofthetangent=(9.4-0.0)/(2200-0)=4.3

10-3(mL/s)112FactorsaffectingtherateofareactionConcentration——Ratelaw速率方程Temperature——ArrheniusEquation阿累尼烏斯方程式CatalystsThephysicalstateofthereactants122-1Concentration白磷在純氧氣中燃燒白磷在含20%的氧氣中燃燒Therelationshipbetweentherateandtheconcentrationsofreactantsiscalledtheratelawforthereaction.Itisdeterminedfromtheexperimentaldata.——初始速率法

13Example7-2400℃,CO(g)+NO2(g)=CO2(g)+NO(g)No.[CO]ini.

(mol/L)[NO2]ini.(mol/L)r0

(mol·L-1·s-1)10.100.100.00520.200.100.01030.300.100.01540.100.200.01050.100.300.015r∝[CO][NO2]r=k[CO][NO2]=0.5[CO][NO2]初始速率法14

Example7-3800℃,2H2+2NO=2H2O+N2

No.[NO](mol/L)[H2](mol/L)rN2(mol·L-1·s-1)16.00

10-31.00

10-33.19

10-326.00

10-32.00

10-36.36

10-336.00

10-33.00

10-39.56

10-341.00

10-36.00

10-30.48

10-352.00

10-36.00

10-31.92

10-363.00

10-36.00

10-34.30

10-3r∝[H2][NO]2

r=k[H2][NO]2=8.86

104[H2][NO]215aA+bB+

gG+hHrate=k[A]

[B]

iscalledtheorderofAand

theorderofB;

+

=n,niscalledreactionorder(thesumofexponentsintherateequation).

kiscalledrateconstantforthereaction.Theunitofkisdeterminedbythereactionordern.Unit：(mol·L-1)1-n·s-1or(mol·dm-3)1-n·s-116n（mol·L-）1-n·s-1

Examples0mol·L-1·s-1

2NH3(g)

N2(g)+3H2(g)1s-1

C12H22O11（sucrose）+H2O

C6H12O6+C6H12O6（fructose）2mol-1·L·s-1

S2O82-+3I-

2SO42-+I3-3mol-2·L2·s-1

2

H2

+

2

NO

2

H2O+

N2

17Mechanism機理Elementaryprocess(基元反應):reactiontakesplaceinonestep.Forexample,singlemoleculereaction:SO2Cl2

SO2+Cl2Doublemoleculereaction:2NO2

2NO+O2

Non-elementaryprocess/complexreaction(非基元反應/復雜反應)reactiontakesplaceinmorethanonestep,whichiscomposedoftwoormoreelementaryprocesses.Forinstance,2NO2(g)+F2(g)

2NO2F(g)theexperimentallyobservedratelawisr=k

[NO2][F2]NO2+F2

NO2F+F(slow,k1)F+NO2

NO2F(fast,k2)18Inaseriesofsteps,thesloweststepdeterminestheoverallrate,whichiscalledtherate-determiningstep.SpecieslikeF,whichisformedinonestepandusedupinanotherstep,iscalledintermediate.Itisobviousthatforelementaryreaction,itsratelawcanbewrittendirectly,butfornon-elementaryreaction,itsratelawcanonlybedeterminedbyexperiments.19設(shè)一級反應式為：AP反應物濃度與反應時間的關(guān)系20lnc-t21

當反應物A的轉(zhuǎn)化率為50%時所需的反應時間稱為半衰期，用表示。

一級反應的半衰期為：則半衰期：22零級、一級、二級反應的速率方程總結(jié)232-2Temperatures

(1)Relationshipsbetweenthereactionrateandtemperature

Figure7-2Differenttypesoftheratechangeswithtemperature24(2)ArrheniusEquationA—指前因子Ea—反應的活化能，單位為kJ·mol-12526Example7-42N2O5(g)

2N2O4(g)+O2(g)T1=298K,k1=3.4×10-5s-1,T2=328K,k2=1.5×10-3s-1.Calculate:EaandA.SOLUTION∵Ea=2.303RT1T2/(T2-T1)·lgk2/k1

=2.303×8.314×298×328/(328–298)·lg1.5×10-3/3.4×10-5=102597(J/mol)

103(kJ/mol)∵lgk=-Ea/2.303RT+lgA∴l(xiāng)gA=13.6A=3.98×1013(s-1)

27Figure7-3Therelationbetweenrateconstantandtemperature28

2-3Reactantstate(反應物之間接觸情況)

Finelydividedironburnsinairbutamassivepieceofironsuchasafryingpandoesnot.

293Fe(s)+4H2O(g)

Fe3O4(s)+4H2(g)

納米技術(shù)與納米材料（尺寸1~100nm,1nm=10-9m）302-4Catalysts

Catalystsareusuallyveryspecific.CO(g)+3H2(g)=CH4(g)+H2O(g)(Nicatalyst)CO(g)+2H2(g)=CH3OH(g)(ZnO-Cr2O3catalyst)

31Catalystsareclassifiedashomogeneousorheterogeneouscatalysts.Homogeneouscatalystsarepresentinthesamephaseasthereactants.Cata1ysisofthedecompositionofozonetooxygenbynitricoxideintheupperatmosphere,2O3=3O2(NO(g)ascatalyst)Thecatalystinacatalyticconverterisaheterogeneouscatalyst.Aheterogeneouscatalystisinadifferentphasefromthereactants.32Cutawayofautomotivecatalyticconvertershowingoutercover,insulator,andceramiccatalyst,whichconsistsofparticlesofplatinum,palladium,andrhodiumdepositedinaceramichoneycomb.333TheoryofReactionRates3-1

CollisionTheoryThecollisiontheoryisbasedonthekinetic-moleculartheory.(1)Theorymodel：consideringreactantmoleculesasrigidballswithoutinternalstructures.

(2)Keypoint：reactantmoleculesmustcollideeachothertoreact.Thereactionrateisproportiontothecollisionfrequencyinunittimeandunitvolume.r

Z。反應速率∝碰撞次數(shù)∝反應物濃度34Firstistheenergyfactor.Onlycollisionsamongactivemolecules(withenergymorethantheactivationenergy)canbringaboutproducts.Heretheactivationenergyreferstotheminimumvaluethatanactivemoleculehas.Ataconstanttemperature,thepercentageofactivemoleculesiscertainanditincreaseswiththetemperature.frepresentsthe

activemoleculepercentage(活化分子百分數(shù)).r

Z·f.

35

Secondistheorientationfactor.Onlywhenactivemoleculescollideincorrectdirectionscancausetheproducts.Prepresentstheorientationfactor.r

P·Z·fForexample,NO2(g)+CO(g)=NO(g)+CO2(g)36

(3)

ApplicationsTheCollisionTheoryexplainstheeffectofreactantconcentrationsandtemperatureontherate.(4)EvaluationsThecollisiontheoryissimpleandclear,yetjustbecauseitistoosimple,itcannotexplaincomplicatedreactionratesinvolvedcomplexmolecules.373-2ActivatedComplexTheoryReactivecollisionbetweenNOandO3molecules.(a)Reactants(b)Activatedcomplex(c)Products3839?rHm=Ea(forward)-Ea(reverse)

Keypoint

反應物分子相互接近時，化學鍵重排，能量重新分配，形成活化配合物，