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1、Reaction Kinetics (1) Xuan ChengXiamen UniversityPhysical ChemistryPhysical Chemistry1Physical ChemistryPhysical ChemistryReaction KineticsFor example-16.63-237.19Thermodynamics: spontaneous reactions (possible to take place)Thermodynamics: cant answer (1) how to make them happen (2) how fast they w
2、ill take place (3) the reaction mechanismReaction KineticsReaction Kinetics2Physical ChemistryPhysical ChemistryReaction KineticsT, P, catalystT, catalystChemical Kinetics:Chemical KineticsThe study of the rates and mechanisms of chemical reactionsA reacting system is not in equilibriumReaction Kine
3、ticsReaction Kinetics3Physical ChemistryPhysical ChemistryRate of ReactionConsider the homogeneous reaction (occurs entirely in one phase)(17.1)The rate of conversion J(17.2)At equilibrium, J = 0Reaction KineticsReaction Kinetics4Physical ChemistryPhysical ChemistryRate of Reaction(17.3)(17.4)*At co
4、nstant VThe rate of reaction rmol dm-3 s-1mol cm-3 s-1Reaction KineticsReaction Kinetics5Physical ChemistryPhysical ChemistryRate LawsFor many reactions (17.5)*k: rate constant (rate coefficient), k = f (T, P), , : order or partial order+ + + n : overall orderThe expression for The expression for r
5、r as a function of concentrations as a function of concentrations at a fixed temperature is called the rate law.at a fixed temperature is called the rate law.Reaction KineticsReaction Kinetics6Physical ChemistryPhysical ChemistryReaction OrdersZero-orderFirst-orderSecond-orderThird-orderNegative Fir
6、st-order1.5-orderNo simple orderReaction KineticsReaction Kinetics7Physical ChemistryPhysical ChemistryRate LawsReaction Rate LawReaction KineticsReaction Kinetics8Physical ChemistryPhysical ChemistryReaction Mechanisms(17.7)intermediate(17.8)Step (a)Step (b)Step (c)Elementary reactionReaction actua
7、lly occursReaction KineticsReaction Kinetics9Physical ChemistryPhysical ChemistryMeasurement of Reaction RatesChemical MethodThe concentration of a reactant or product as a function of timeReaction vesselsAt constant TAt intervalsSlows down or stop the reactionRapidly analyze chemical compositions o
8、f the mixtureCooling the sampleremoving a catalystDiluting the mixtureAdding a speciesReaction KineticsReaction Kinetics10Physical ChemistryPhysical Chemistry反应速率的测定方法化学方法 不同时刻取出一定量反应物，设法用骤冷、冲稀、加阻化剂、除去催化剂等方法使反应立即停止，然后进行化学分析。Reaction KineticsReaction Kinetics11Physical ChemistryPhysical ChemistryMeas
9、urement of Reaction RatesPhysical MethodMeasures a physical property of the reaction system as a function of time. This allows the reaction to be followed continuously as it proceeds.More accurate and less tedious物理方法 用各种物理性质测定方法（旋光、折射率、电导率、电动势、粘度等）或现代谱仪（IR、UV-VIS、ESR、NMR、ESCA等）监测与浓度有定量关系的物理量的变化，从而求
10、得浓度变化。物理方法有可能做原位反应。Reaction KineticsReaction Kinetics12Physical ChemistryPhysical ChemistryIntegration of Rate LawsAssumptions(a) The reaction is carried out at constant temperature (k is constant)(b) The volume is constant (r is given by (17.4)(c) The reaction is “irreversible” (ko is very large)(1
11、7.4)*Integrate it to find A as a function of time: A = g(t)Reaction KineticsReaction Kinetics13Physical ChemistryPhysical ChemistryFirst-Order ReactionsSuppose the reactionis first-order with(17.4)*(17.5)*(17.10)define(17.11)Reaction KineticsReaction Kinetics14Physical ChemistryPhysical ChemistryFir
12、st-Order Reactions(17.12)(17.13)ifatatand(17.14)*The concentration of A (and r) decreases exponentially with time for a first-order reaction.(17.10)Integrated rate lawReaction KineticsReaction Kinetics15First-order reaction: lnA vs tFirst-Order ReactionsPhysical ChemistryPhysical Chemistry(17.14)*A/
13、AotFirst-order reaction: A/Ao vs tLnAtReaction KineticsReaction Kinetics16First-Order ReactionsPhysical ChemistryPhysical ChemistryHalf-life:(17.13)First-order reaction(17.15)*The time needed for A to drop to half its valueIndependent of AoA useful indication for the chemical reaction rateReaction K
14、ineticsReaction Kinetics17Second-Order ReactionsPhysical ChemistryPhysical Chemistry(17.10)define(17.11)Reaction KineticsReaction Kinetics18Second-Order ReactionsPhysical ChemistryPhysical Chemistry(17.16)A plot of 1/A versus t gives a strait line of slope kA if (17.17)Reaction KineticsReaction Kine
15、tics19A-1tSecond-order reaction: 1/A vs tSecond-Order ReactionsPhysical ChemistryPhysical Chemistry(17.16)Half-life:Second-order reaction with r = kA2Reaction KineticsReaction Kinetics20Second-Order ReactionsPhysical ChemistryPhysical ChemistrySecond-order reaction with r = kA2First-order reaction w
16、ith r = kA(17.18)Three variablesReaction KineticsReaction Kinetics21Second-Order ReactionsPhysical ChemistryPhysical Chemistryx=0 when t=0Reaction KineticsReaction Kinetics22Second-Order ReactionsPhysical ChemistryPhysical Chemistry(17.22)Reaction KineticsReaction Kinetics23Second-Order ReactionsPhy
17、sical ChemistryPhysical ChemistryIf Ao=Bo(17.23)Half-life:Reaction KineticsReaction Kinetics24Third-Order ReactionsPhysical ChemistryPhysical Chemistry(Problems 17.17 and 17.24)(17.24)Reaction KineticsReaction Kinetics25nth-Order ReactionPhysical ChemistryPhysical ChemistryConsider (17.25)Integratio
18、n gives(17.26)For n 1(17.27)For n 1(17.28)Reaction KineticsReaction Kinetics26nth-Order ReactionPhysical ChemistryPhysical Chemistry(17.29)For n 1For n = 1(17.30)Half-life:(17.26)For n = 0Reaction KineticsReaction Kinetics27HomeworkPhysical ChemistryPhysical ChemistryPage 591Prob. 17.5Prob. 17.6Prob. 17.8Prob. 17.10Reaction KineticsReaction Kinetics28
