Chapter Five Rates of Chemical ReactionChemical ReactionWeather can occur?-chemical thermodynamicsHow fast(reaction rate)?-chemical kinetics 反应机理：反应机理：化学反应所经历的化学反应所经历的途径途径或或具体步骤具体步骤，又又称为称为反应历程反应历程化学反应化学反应速度的快慢速度的快慢 主要决定于反应的主要决定于反应的内在机理内在机理化学动力学的基本任务就是研究反应的机理化学动力学的基本任务就是研究反应的机理l某一反应究竟是经过哪些步骤完成的，某一反应究竟是经过哪些步骤完成的，l了解各个步骤的特征和相互联系，了解各个步骤的特征和相互联系，l揭示化学反应速度的本质，使人们能够揭示化学反应速度的本质，使人们能够自觉控制反应速度自觉控制反应速度反应机理可以告诉我们：反应机理可以告诉我们：问题问题1.为什么有些口服药物的服用方法是2次/天？3次/天?2.为什么静脉滴注某些青霉素类药物要加快滴注的速度？二、酶作为生物催化剂的特性：2.)5-1 Rates and Mechanisms of Chemical Reactions 5-2 Theories of Reaction Rate 5-3 Reaction Rates and Concentrations 5-4 Effect of Temperature on Reaction Rates5-5 Effect of Catalyst on Reaction Rates Chapter Five Rates of Chemical ReactionReaction rate:changes in a concentration of a product or a reactant per unit time.tcvThe rate is defined to be a positive number.The unit of reaction rate is molL-1S-1,molL-1min-1 or molL-1h-1 et al5-1 Rates and Mechanisms of Chemical Reactionsaverage reaction rate is obtained by dividing the change in concentration of a reactant or product by the time interval over which the change occurs4)-(5 tcvDefine reaction rate:2N2O5 =4NO2+O21.Average reaction rateSAMPLE EXERCISE:H2O2=H2O+1/2 O2 0:c1(H2O2)=15.8810-3 mol/L 5:c2(H2O2)=12.810-3 mol/L )(106.05100.3)(1133121222sLmolttcctcOHv)(103.05105.1)(113312122sLmolttcctcOvSo:Reaction Rates and StoichiometryH2O2=H2O+1/2 O2tOtOHtOHrate212222用不同物质浓度变化所表示的反应速率之间存在着一定的关系是：它们之间的速率比正好等于反应式中各物质分子式的系数之比，lTo generalize,for the reactionaA+bB cC+dDThis equation can be used to establish the relationship between rate of change of one reactant or product to another reactant or product.nYou have to be able to do this on the test,too!tct2.Instantaneous reaction rateThe instantaneous rate of change at a point is the same as the slope of the tangent line.That is,its the slope of a curve.V=lim =-ct0t dcdtcvdtOdvdtOHdv 222Define reaction rate:2N2O5 =4NO2+O25-1.2 The Mechanisms of Chemical ReactionsA reaction mechanism is a description of the path that a reaction takes.lelementary reaction？loverall reaction？ltypes of elementary reactions5-1.2 The Mechanisms of Chemical Reactions elementary reaction:is one that the reactants can convert directly into the products in a single step when they act each other.(one-step reaction)基元反应：基元反应：反应物间相互作用直接转化为生成物的反应。
反应物间相互作用直接转化为生成物的反应简称元反应）简称元反应）MClM2ClClHClClHHHClH ClM2ClMCl2222例如：overall reaction:Many reactions are actually made up of several elementary steps,which are combined to yield the overall reaction.NO2+CO NO+CO2NO2+NO2 NO3+NO (slow)NO3+CO NO2+CO2 (fast)This means that the rate of the overall reaction is dominated（控制）（控制）by the rate of the first reaction,this is the rate-determining step.H2(g)+I2(g)2 HI(g)I2(g)2I (fast)H2+2I 2HI (slow)rate-determining step.Types of Elementary Reactionsunimolecular reaction:an elementary reaction in which the rearrangement of a single molecule produces one or more molecules of product.I2(g)2I(g)bimolecular reaction:the collision and combination of two reactants to give an activated complex in an elementary reaction.NO(g)+O3(g)NO2(g)+O2(g)l molecularity-for Elementary Reactions:_ termolecular reaction:an elementary reaction involving the simultaneous collision of any combination of three molecules,ions,or atoms.2 NO+H2 N2+H2O25-2 Theories of Reaction RatelOne is the collision theory:The collision theory is based on the kinetic theory and assumes a collision between reactants before a reaction can take place.1918年年 Lewis以气体分子运动论为基础提出以气体分子运动论为基础提出lAnother is the transition state theory:The transition state theory suggests that as reactant molecules approach each other closely they are momentarily in a less stable state than either the reactants or the products.Contents of Collision Theory:reacting molecules must come so close that they collide.effective collisions:not every collision between molecules creates products,only few collisions between reactant molecules will react.5-2.1 Collision Theory and Activation Energy Contents of Collision Theory:lAccording to this theory,product formation can only take place when there are effective collisions between reactant molecules involved in the rate determining step of the process.Br(g)+HI(g)HBr(g)+I(g)lStraight on collision,hydrogen facing incoming bromine.Reaction occurs.lStraight on collision,hydrogen facing away from incoming bromine.Reaction does not occur.lStraight on collision,bromine at 90 degrees.Reaction does not occur.What constitutes an effective collision?发生有效碰撞的两个基本前提发生有效碰撞的两个基本前提:enough energy 对对 HCl 和和 NH3 的气相反应的气相反应 proper orientation Activation molecule:lthe average molecules must absorb some energy to become activation molecules is the molecule have enough energy and can produce effective collision 活化分子一般只占极少数，它具有的最低能量为Ec。
通常把活化分子具有的平均能量与反应物分子的平均能量之差称为反应的活化能，用符号 Ea 表示kcaEEE 在一定温度下，反应的活化能越大，活化分子的分子分数越小，活化分子越少，有效碰撞次数就越少，因此化学反应速率越慢；反应的活化能越小，活化分子的分子分数越大，活化分子越多，有效碰撞次数就越多，化学反应速率越快Figure:As the activation energy of a reaction decreases,the number of molecules with at least this much energy increases,as shown by the yellow shaded areas.离子反应和沉淀反应的离子反应和沉淀反应的Ea都很小都很小 一般认为一般认为Ea小于小于63 kJmol-1的为快速反应的为快速反应 小于小于40 kJmol-1和大于和大于400 kJmol-1的都很难测定出的都很难测定出 一些反应的一些反应的Ea 每一反应的活化能数值各异每一反应的活化能数值各异,可以通过实验和计算得可以通过实验和计算得 到到活化能越小活化能越小,反应速率越快。
反应速率越快Ea是动力学参数是动力学参数N2(g)+3H2(g)=2NH3(g),Ea=175.5 kJmol-1HCl+NaOH NaCl+H2O,Ea20 kJmol-12SO2(g)+O2(g)=2SO3(g),Ea=251 kJmol-11-r223molkJ6.199-(g)O(g)NONO(g)(g)O=+=+H 反应物的能量必反应物的能量必 须爬过一个能垒须爬过一个能垒 才能转化为产物才能转化为产物 即使是放热反应即使是放热反应 (rH为负值为负值)，外界仍必须提供外界仍必须提供 最低限度的能量，最低限度的能量，这个能量就是这个能量就是 反应的活化能反应的活化能 5-2.2 The Transition State TheoryTransition state theory(TST)is also called activated complex theory.reactants pass through high-energy transition states before forming products,they are associated in an unstable entity called an activated complex,then change into products.要点：化学键重排、活化络合物形成 Example:NO2(g)+CO(g)NO(g)+CO2(g)H=Ea,f-Ea,r =358 kJmol-1-132 kJmol-1 H=226kJmol-1.酶作用的机制中间产物学说 酶与底物形成酶底物中间复合物，中间复合物再分解成产物和酶。
E +S =E-S E +S =E-S P +E P +E 许多实验事实证明了ES复合物的存在理论受限理论受限 活化络合物的结构无法在实验中加以确定活化络合物的结构无法在实验中加以确定 计算过于复杂计算过于复杂Factors That Affect Reaction RateslConcentration of ReactantslTemperaturelCatalysts _Speed by changing mechanism 5-3 Reaction Rates and ConcentrationsChemical reactions are faster when the concentrations of the reactants are increased.Because more molecules will exist in a given volume.More collisions will occur and the rate ofa reaction will increase.Concentration and RateEach reaction has its own equation that gives its rate as a function of reactant concentrations.this is called its Rate Law说明在一定温度下，反应速度与反应物浓度之间的定量关系说明在一定温度下，反应速度与反应物浓度之间的定量关系 质量作用定律质量作用定律A rate law shows the relationship between the reaction rate and the concentrations of reactants.5-3.1 The Rate LawvAmBnaA +bB cC+dDv=kAmBn反应速率方程或称质量作用定律反应速率方程或称质量作用定律The rate of a reaction is proportional to the product of the concentrations of the reactants raised to some power.v=kAmBnk is a rate constant that has a specific value for each reaction.The value of k is determined experimentally.“Constant”is relative here-k changes with T，the unit(量纲)depend on m+n when A=B=1molL-1,v=k the greater the k,the faster the rate 参见中文P101质量作用定律（质量作用定律（law of mass action）对于基元反应，对于基元反应，反应速率与反应物浓度的幂反应速率与反应物浓度的幂乘积成正比。
乘积成正比幂幂指数就是指数就是基元反应基元反应方程中各反应方程中各反应物的系数，这就是质量作用定律物的系数，这就是质量作用定律MCl MClM2Cl HCl ClHClClH ClH HHClH Cl MCl M2ClMCl 22222222kvkvk vk v 对于复杂反应，对于复杂反应，它适用于每一步的基元反应，它的反应速它适用于每一步的基元反应，它的反应速度取决于定速步骤度取决于定速步骤2N2O5（g）4NO2（g）O2 (g)实验证明实验证明 N2O5 NO3NO2 （慢）NO2NO3 NO2O2NO （快）NONO3 2NO2 （快）52ONkv 质量作用定律仅适用于基元反应质量作用定律仅适用于基元反应速率方程应为速率方程应为in general,m and n are not equal to the stoichiometric coefficients a and b A,B are the concentration of A and B;m and n are themselves constants for a given reaction,it must be determined experimentallyv=kAmBnaA +bB cC+dDThe order of a reaction with respect to one of the reactants is equal to the power to which the concentration of that reactant is raised in the rate equation.5-3.2 Order of A ReactionThe sum of the powers to which all reactant concentrations appearing in the rate law are raised is called the overall reaction order.m is the order of the reaction with respect to A,n is the order of the reaction with respect to B.For rate equation v=kAmBnthe exponents m and n are not necessarily related to the stoichiometric coefficients in the balanced equation,that is,in general it is not true that for a A+b B c C+d D,m a and n bm+n is overall order of the reactionThe rate law for the thermal decomposition（热分解）（热分解）of acetaldehyde(CH3CHO)CH3CHO(g)CH4(g)+CO(g)has been determined experimentally to be v=kCH3CHO3/2 and not rate=kCH3CHOExample 5-1:Given the following data,what is the rate expression for the reaction between hydroxide ion and chlorine dioxide?2ClO2(aq)+2OH-(aq)ClO3-(aq)+ClO2-(aq)+H2O ClO2(mol.L-1)OH-(mol.L-1)Rate(mol.L-1 s-1)0.010 0.030 6.0010-4 v1 0.010 0.075 1.5010-3 v2 0.055 0.030 1.8210-2 v3 Solution:v=kClO2mOH-n m=?32-23-1 4-112 101.82 0.030 055.0 101.50 0.075 010.0 106.00 0.030 010.0)(vvvsLmolrateOHClOmmmmmClOClOClOClOvv)5.5(3.30)010.0055.0(1000.61082.1)(421232123213By inspection,m=2.The reaction is 2nd order in ClO2 By inspection,n=1 32-23-1 4-112 101.82 0.030 055.0 101.50 0.075 010.0 106.00 0.030 010.0)(vvvsLmolrateOHClOnnnOHOHvv)5.2(5.2)030.0075.0(1000.61050.1)(431212The overall rate expression is therefore v=kClO22OH-v=kClO2mOH-n n=?想一想：想一想：反应速度与速率方程？反应分子数和反应级数？First-order reactionsA first-order reaction is a reaction whose rate depends on the reactant concentration raised to the first power.A Bthe rate equation isckAkv1Differential form:ckdtdcdtAdv1Integrate the left side from c=c0 to c and the right from t=0 to t.ckdtdc1dtkcdc1Thus tccdtkcdc010速度方程的积分表达式速度方程的积分表达式Can be rearranged to give:tkcct10ln-lnc lnc0=k1(t-0)c0 is the initial concentration of c(t=0).c is the concentration of c at some time t.8)-(5 log303.201cctk 9)-(5 log303.2log01ctkcorThe characteristics of first-order reactions：1.A plot of lgc versus t(time)gives a straight line with a slope of -k1/2.303.2.The rate constant,k,has units of time-1.3.half-life(t1/2)is the time it takes for the concentration of a reactant A to fall to one half of its original value.8)-(5 log303.201cctk By definition,when t=t1/2,socckt01log303.2lg2 2.303 2log303.2100121kcckt20cc 恒温下，一级反应的半衰期是一个常数。
恒温下，一级反应的半衰期是一个常数半衰期越长，半衰期越长，k1就越小，反应速率就越慢就越小，反应速率就越慢10)-(5 693.012/1kt可以用半衰期衡量反应速度，可以用半衰期衡量反应速度，t1/2越大，反应越慢越大，反应越慢一级反应的半衰期与速率常数一级反应的半衰期与速率常数k1成反比，成反比，与反应物的起始浓度无关与反应物的起始浓度无关l常见药物的半衰期：常见药物的半衰期：药物名称药物名称 t1/2（h）青霉素青霉素 0.5 链霉素链霉素 23 安定安定 2040放射性同位素放射性同位素14C半衰期为半衰期为5580年年一级反应的特点是：（1）1gc对时间对时间t作图可得一条直线，直作图可得一条直线，直线的斜率为线的斜率为 k1/2.303因此可由因此可由斜率斜率求得反应速率常数求得反应速率常数k12）k1的单位为的单位为时间时间1这说明这说明k1的数值与时间单位有关，的数值与时间单位有关，而与浓度无关而与浓度无关3）恒温下，一级反应的半衰期是与速）恒温下，一级反应的半衰期是与速率常数率常数k1成反比，与反应物的起始浓度成反比，与反应物的起始浓度无关的一个常数无关的一个常数log303.201cctk=12/1693.0ktExample 5-2(a)What is the rate constant k for the first-order decomposition of N2O5(g)at 25 if the half-life of N2O5(g)at that temperature is 4.03104 seconds?Solution:(a)skt42/11003.4693.0)(1072.11003.4693.0693.01542/1stk=-Solution:(b)Putting in the value for k and substituting t=8.64104 seconds(one day has 86,400 seconds)gives 303.2log0ktcc645.0303.21064.81072.1log450cc(b)Under these conditions,what percent of the N2O5 molecules will not have reacted after one day?HenceTherefore,22.6%of the N2O5 molecules will not have reacted after one day at 25.226.00cc226.005252=ONONExample 5-3SO2Cl2（磺酰氯）decomposes to sulfur dioxide and chlorine gas.The reaction is first order.If it takes 13.7 hours for a 0.250mol/L solution of SO2Cl2 to decompose into a 0.117mol/L solution,what is the rate constant for the reaction and what is the half-life of SO2Cl2 decomposition?Solution:303.2loglog0ktcc303.27.13117.0log250.0logkK=0.0554 h-1)(5.120554.0693.0693.02/1hkt一级反应很多，许多热分解反应、分子重排反应、放射一级反应很多，许多热分解反应、分子重排反应、放射性元素的蜕变等都是一级反应，许多化合物的水解反应性元素的蜕变等都是一级反应，许多化合物的水解反应在低浓度的水溶液中进行时也表现为一级反应，在低浓度的水溶液中进行时也表现为一级反应，许多药许多药物在生物体内的吸收、分布、代谢和排泄过程，也常近物在生物体内的吸收、分布、代谢和排泄过程，也常近似地看作是一级反应。
似地看作是一级反应l例例5-2 已知四环素在人体内的代谢服从一级反应规律已知四环素在人体内的代谢服从一级反应规律设给人体注射设给人体注射0.5g四环素，然后在不同时间测定血液中四环素，然后在不同时间测定血液中四环素的含量，得如下数据：四环素的含量，得如下数据：服药后时间服药后时间t/h 4 6 8 10 12 14 16血中四环素含量血中四环素含量c/mgL-1 4.6 3.9 3.2 2.8 2.5 2.0 1.6 试求：试求：四环素代谢的半衰期；四环素代谢的半衰期；若血液中四环素的最低有效量相当于若血液中四环素的最低有效量相当于3.7mgL-1，则需几小时后注射第二次？则需几小时后注射第二次？解：解：先求速率常数先求速率常数k1，一级反应以，一级反应以log c对对t 作图，得直线，作图，得直线，见图见图5-6由前后两点或由直线回归得由前后两点或由直线回归得:038.04166.4lg6.1lg斜率）（-1h088.0)038.0(303.2k(h)9.7088.0693.0 693.012/1kt计算表明：计算表明：要使血液中四环素含量不低要使血液中四环素含量不低 于于3.7mgL-1，应于第一次，应于第一次 注射后注射后6.3h 之前注射第二次，临床上一般控制之前注射第二次，临床上一般控制 在在6h后注射第二次，后注射第二次，即即4次次/天。
天由图由图5-6知，知，t0时，时，lgc00.81，最低有效量，最低有效量c3.7mgL-1 lgc0.57,将将（5-8）重排得：重排得：)(3.6088.0)57.081.0(303.2 )lg(lg303.210hkcct8)-(5 log303.201cctk 另外，衡量药物分解的速率时，常用分解另外，衡量药物分解的速率时，常用分解10所所需的时间，称为十分之一衰期，用需的时间，称为十分之一衰期，用t0.9表示，恒温下表示，恒温下t0.9也是与浓度无关的常数也是与浓度无关的常数119.01054.090100lg303.2kkt 了解药物的半衰期，对于合理用药有着重要意义了解药物的半衰期，对于合理用药有着重要意义常见药物的半衰期，如常见药物的半衰期，如 磺磺胺甲恶唑（新诺明），半衰期胺甲恶唑（新诺明），半衰期12小时左右小时左右；头孢氨苄头孢氨苄，半衰期为半衰期为12小时小时；地西泮为地西泮为2040h，保泰松为保泰松为48120hSecond-order reactions22ckdtdcvv=k2A2,v=k2 AB A=Bdtkcdc 22二级反应是一类常见的反应，溶液中的许多有机反应二级反应是一类常见的反应，溶液中的许多有机反应像像加成、取代加成、取代及及消去消去反应等都是二级反应。
反应等都是二级反应11)-(5 1120tkcc0211ctkc)11(102cctkThe integrated rate law for a 2nd order reaction can be easily shown to be tccdtkcdc0220The characteristics of second-order reactions：1.A graph of 1/c against time is a straight line,the slope of which gives the rate constant for the reaction；2.The rate constant,k,has units of c-1t-1；3.The half-life of 2th-order reactions)11(102cctk(c=2/c0代入上式)t1/2=1/kc0.Note that the half-life of a second-order reaction is not independent of the initial concentration,as in the case of a first-order reaction.This is one way to distinguish a first-order reaction from a second-order reaction.（1）1/c对时间对时间t作图可得一条直线，作图可得一条直线，直线的斜率即为反应速率常数直线的斜率即为反应速率常数k2。
2）k2的单位为的单位为浓度浓度-1时间时间-1k2的数值与时间和浓度单位有关的数值与时间和浓度单位有关3）二级反应的）二级反应的 由此可见：二级反应由此可见：二级反应 的半衰期与反应物的初始浓度成反比的半衰期与反应物的初始浓度成反比反应物初始反应物初始 浓度越大，半衰期越短浓度越大，半衰期越短022/11ckt二级反应有以下特点是：二级反应有以下特点是：Solution:t=3.6(min)tkcc2011t84.0500.01200.01Example 5-4Example 5-4Butadiene(CButadiene(C4 4H H6 6丁二丁二烯烯)dimerizes)dimerizes(聚合聚合)to form C)to form C8 8H H1212（二（二聚物）聚物）.This reaction is 2nd order in butadiene.If the rate.This reaction is 2nd order in butadiene.If the rate constant for the reaction is constant for the reaction is 0.84 Lmol0.84 Lmol-1-1minmin-1-1,how long,how long will it take for a 0.500 mol/L sample of butadiene to will it take for a 0.500 mol/L sample of butadiene to dimerizedimerize until the butadiene concentration is 0.200 mol until the butadiene concentration is 0.200 mol/L?/L?（5-11）例例5-3乙酸乙酯在乙酸乙酯在25时的皂化反应为二级反应：时的皂化反应为二级反应：CHCOOCH十十NaOHCHCOONa十十CHOH 乙酸乙酯和氢氧化钠的起始浓度均为乙酸乙酯和氢氧化钠的起始浓度均为0.0100molL，反，反应应20min后，氢氧化钠的浓度消耗了后，氢氧化钠的浓度消耗了 0.00566molL，求：求：反应速率常数；反应速率常数；反应的半衰期。
反应的半衰期解：解：)11(102cctk11min52.60100.0100566.00100.01201Lmol022/11cktmin3.150100.052.61 Zero-order reactions is one where the rate does not depend on the concentration of the species.000ckdtdcvv=k0 A0tkcc00integrated：tccdtkdco00固体界面上的分解反应固体界面上的分解反应 c=-k0 t+c0 c=-k0 t+c01.A graph of c against t is a straight line with a slope of -k0.The characteristics of zero-order reactions：2.The rate constant,k,has units of c t-1；3.The half-life of a zero-order reaction is 00002/15.02kckct（1）c对对t作图得一直线，斜率为作图得一直线，斜率为k0（2）k0的单位为浓度时间的单位为浓度时间 所以所以k k0 0与时间单位和浓度单位有关与时间单位和浓度单位有关（3）零级反应的半衰期：）零级反应的半衰期：所以零级反应的半衰期与最初浓度成正比。
所以零级反应的半衰期与最初浓度成正比反应物的初始浓度越大，半衰期越长反应物的初始浓度越大，半衰期越长00002/15.02kckct近年来发展的一些缓解长效药，其释药速率在相当长的时间范近年来发展的一些缓解长效药，其释药速率在相当长的时间范围内比较恒定，即属零级反应如国际上应用较广的一种皮下围内比较恒定，即属零级反应如国际上应用较广的一种皮下植入剂，内含女性避孕药左旋植入剂，内含女性避孕药左旋18甲基炔诺酮，每天约释药甲基炔诺酮，每天约释药30g，可一直维持，可一直维持5年左右零级反应的特点：零级反应的特点：The decomposition of HI into hydrogen and iodine on a gold surface is 0th order in HI.The rate constant for the reaction is 0.050molL-1s-1.If you begin with a 0.500mol/L concentration of HI,what is the concentration of HI after 5 seconds?Solution:HI =0.5000.0505 =0.250(molL-1)0cktcc0=0.500molL-1 k=0.050molL-1 s-1 t=5sExample 5-55-4 Effect of Temperature on Reaction RatesChemical reactions are faster when the temperature is increased.Why?Figure:At a higher temperature,T2,more molecules have an energy greater than E a,as shown by the yellow shaded area.When we increase the temperature,kinetic energies and speeds will increase and so the average energy of a collision will also increase.As a result,the energy of any particular collision will be more likely to exceed the activation energy.Thus,chemical reactions are faster at higher temperatures than at lower temperatures.lThe dependence of reaction rate on temperature has led to a common rule of thumb:the rate of a chemical reaction will double for each 10 increase in the temperature.Rule of thumb：5-4.1 Rule of Thumb经验法则经验法则(Vant Hoff Law)The rate of a chemical reaction will double foreach 10 increase in the temperature.v(T+10)k(T+10)=-=-=24 v T k T a A+b B=c C+d D T:v T=k T Aa Bb(T+10):v(T+10)=k T+10 Aa Bb5-4.2 The Arrhenius EquationIn 1889 Svante Arrhenius showed that the dependence of the constant of a reaction on temperature can be expressed by the following equation,now known as the Arrhenius equationl通过实验制作速率常数k随温度T升高而变大的曲线图，并分析曲线，可以得出速率常数随温度变化函数的经验方程:RTEaAek/Ea is the activation energy of the reaction(in kJ/mol)R is the gas constant(8.314 JK-1molmol-1-1)T is the absolute temperature e is the base of the natural logarithm scale A represents the collision frequency,and is called the frequency factor(指前因子指前因子).The Arrhenius Equation:阿伦尼乌斯方程式的阿伦尼乌斯方程式的重要假设重要假设：A和和Ea是是不随温度改变不随温度改变的特征参数。
的特征参数大多数反应在一定大多数反应在一定温度区间内温度区间内的这种近似是完全允许的，这种近似方的这种近似是完全允许的，这种近似方法被称为线性化法被称为线性化1）对某一反应：）对某一反应：Ea基本不变，温度升高，基本不变，温度升高，增大，增大，k值也增大，反应速率加快，说明了温度对反应速率的影值也增大，反应速率加快，说明了温度对反应速率的影响2）对不同反应：）对不同反应：当温度一定时，活化能当温度一定时，活化能Ea值越小，值越小，则则 越大，越大，k值愈大，反应速率愈快值愈大，反应速率愈快反之，反之，Ea愈大，反应速率愈慢愈大，反应速率愈慢)/(RTEae)/(RTEae阿伦尼乌斯方程式把阿伦尼乌斯方程式把速率常数速率常数k k、活化能活化能E Ea a和和温度温度T T三者联系起来，由此关系式可三者联系起来，由此关系式可以说明：以说明：RTEaAek/ATREkalg)1(303.2lgTaking the natural logarithm of both sides,the equation becomesor in terms of common logarithms:RTEaAek/Example 5-6The rate constants for the decomposition of acetaldehyde CH3CHO(g)CH4(g)+CO(g)were measured at five different temperatures.The data are show below.Plot lgk versus 1/T and determine the activation energy(in KJ/mol)for the reaction.T(K)700 730 760 790 810 k 1/(mol/L)1/2s 0.011 0.035 0.105 0.343 0.789 Answer:We need to plot lg k versus 1/T.From the given data we obtain 1/T(1/K)1.4310-3 1.3710-3 1.3210-3 1.2710-3 1.2310-3log k -1.96 -1.46 -0.979 -0.465 -0.103The slope of the line is calculated from two pairs of coordinates:31025.1 ;30.031041.1;80.1ATREkalg)1(303.2lglg k1/TThus,a plot of lg k versus 1/T gives a straight line whose slope is equal to-E a/2.303R and whose intercept（截距）（截距）with the ordinate(纵坐标纵坐标)is log A.Ea=2.303(8.314J/Kmol)(9.38103K)=1.80105 J/mol =1.80102 KJ/mol5-4.3 Application of Arrhenius EquationT1 k1According to this equation,we can calculate E a and kT2 k213)-(5 303.2loglg11RTEAka14)-(5 303.2loglg22RTEAka155 11303.2lg1221TTREkka(5-14)-(5-13)：Example 5-7The rate constant of a first-order reaction is 3.4610-2/s at 298 K.What is the rate constant at 350 K if the activation energy for the reaction is 50.2 KJ/mol?Answer:29813501314.8303.2102.501046.3log322k155 11303.2log1221TTREkka31.11046.3log22k)(71.012sk5-5 Effect of Catalyst on Reaction Ratesl Catalyst:a substance that increase the rate of a chemical reaction,but is itselfneither consumed nor produced in the reactionMnO2 Catalysts increase the rate of a reaction by decreasing the activation energy of the reaction.Catalysts change the mechanism by which the process occurs.Reaction O3 +O =O2 three typeshomogeneous(均相均相)catalysis,heterogeneous(非均相)catalysisenzyme catalysis.Catalysis can be classified intol Homogeneous catalysislIn homogeneous catalysis,the catalyst is present in the same phase as the reactants,las when a gas-phase catalyst speeds up a gas-phase reaction,or a species dissolved in 。