songhui化学反应速率

1、1会计学songhui化学反应速率化学反应速率productreactant ccvvtt The change in the concentration of reactant or product during a time ductreactant ccvvtt Change in the concentration of speciesChange in timeV The change in the concentration of reactant or product at one specific instant time. 在反应时在反应时间间隔无限小

2、时，反应物浓度或生成物浓度的间间隔无限小时，反应物浓度或生成物浓度的变化与时间间隔的比值变化与时间间隔的比值ractantproductproductreactant dcdcvvdtdtH2O2(aq)H2O(l) +12O2(g)I-22220(H O )d (H O )limdtccvtt ,0BBBBBnnnproductreactant11BBBBBBdcdcdndcdvV dtVdtdtdtdt 单位体积内反应进度随时间变化率单位体积内反应进度随时间变化率此时的此时的v v代表整个化学反应的速率，与反应体系代表整个化学反应的速率，与反应体系中选择何种物质表示反应速率无关中选择何种物

3、质表示反应速率无关例： N2 + 3H2 2NH3322d (NH )d (N )d (H )11d3d2dcccvttt aA + bB = cC + dD1(A)1(B)1(C)1(D)dcdcdcdcvadtbdtcdtddt ABCreactantproductreactElementary reaction ：ABReactantsIntermediate productreactEnd productMultistep mechanisms (composite reaction)非元反应（复合反应）非元反应（复合反应）The sum of the stoichiometric c

4、oefficient of the reactants in elementary reaction.元反应中反应物系数之和称反应分子数元反应中反应物系数之和称反应分子数单分子反应单分子反应:If a single molecule is involved, the reaction is said to be unimolecular.H3CNCH3CCNH3CCNmethyl isonitrile rearrange1NO2+ 1CO = NO + CO22NO + 1H2 = N2O + H2O 2I + 1H2 = 2HI三分子反应三分子反应: :Elementary steps in

5、volving the simultaneous collision of three molecules are said to be termolecular reaction双分子反应双分子反应: :Elementary steps involving the collision of two reactant molecules are said to be bimolecular reaction（注意：反应分子数仅适用于元反应）（注意：反应分子数仅适用于元反应）The process by which a reaction occurs is called reaction mec

6、hanism . It involve one or more intermediates化学反应进行的实际步骤。即实化学反应进行的实际步骤。即实现化学反应的各步元反应组合的微观过程现化学反应的各步元反应组合的微观过程The slowest step in mechanism.在化学反应的实际步骤中，由许多元反应组成在化学反应的实际步骤中，由许多元反应组成，其中最慢的那步元反应限制着整个复杂反应，其中最慢的那步元反应限制着整个复杂反应的速率大小，这一较慢的元反应称为的速率大小，这一较慢的元反应称为速率控制速率控制步骤步骤，简称，简称速控步骤速控步骤(a)弹性碰撞弹性碰撞 (b)有效碰撞有效碰撞

7、 反应物分子互相接近，发生碰撞，碰撞后发生反应物分子互相接近，发生碰撞，碰撞后发生化学反应化学反应仅有分子间的能量交换，不发生化学反应仅有分子间的能量交换，不发生化学反应H2 + I2 HI At room temperature the reaction proceeds very slowly . Only about 1 in every 1013 collisions produces a reaction effective collision . Each molecule undergoes about 1010 collisions per secondFor example

8、(1) The molecules of the reactant must have enough energy. to stretch, bend, and ultimately break bonds, leading to chemical reactions.(1)(1)反应物分子要有足够高的能量反应物分子要有足够高的能量以克服分子或离子外层价电子云间的排斥力以克服分子或离子外层价电子云间的排斥力而充分接近，产生电子重排，使旧的化学键而充分接近，产生电子重排，使旧的化学键破裂，而形成新的化学键，即形成新的分子破裂，而形成新的化学键，即形成新的分子(2) 具有高能量的分子间碰撞要有合适

9、方向具有高能量的分子间碰撞要有合适方向 分子在碰撞时，只有相互反应的原子碰分子在碰撞时，只有相互反应的原子碰撞在一起才可能发生化学反应，才能使分子撞在一起才可能发生化学反应，才能使分子或离子的反应部位间旧键破裂，新键形成或离子的反应部位间旧键破裂，新键形成OCOONO NO C OCollisions must occur not only with sufficient energy but also with suitable orientation to cause reaction.E平均平均EEa活化分子活化分子动能动能ENNEa2Ea1Activated moleculesKine

10、tic energyENNEaEaaERTfe有效碰撞频率总碰撞频率aERTvZ P fZ P eThe activated complex is not a stable molecule, and so it exists for only an instant before flying apart one way or the other. It flies apart because its potential energy is higher than that of either the reactant or the product molecules. Give out en

11、ergyAbsorbenergyA |AB |B+AABB2A-B orA-A+B-B分子变化分子变化能量变化能量变化Kinetic energyPotential energy反应进程反应进程ReactantActivated complex Productor reactantKinetic energyH反应进程的势能图反应进程的势能图A2+B2Reactants 2ABProductsEbEbComplex actived Potential energyE=H0 Exothermic reaction放热反应放热反应H3CCNH3CCNPotential energyH02CDRea

12、ction coordinatePotential energy(b)Figure5-7 Potential-energy changes during the course of a reaction: (a) Exothermic reaction. (b) Endothermic reaction.Ea EaEa 吸热反应吸热反应Ea The effect of the concentration on the reaction ratetan productreactCCvvtt NO2(g)+CO(g)NO(g)+CO2(g) When the temperature is fixe

13、d , the rate of a elementary reaction is proportional to the product of the molarity of the reactants , each raised to the power of its stoichiometric coefficient in the equation of the elementary reaction .2N2O5(g)4NO2(g)+O2(g) (3) The number of k amount to the number of rate when the concentration

14、 of every reactant is 1 molL-111ababABvvkvC C k is called specific rate(1)The rate law only can be applied to elementary reaction.只有元反应，才可利用质量作用定律直接写出速只有元反应，才可利用质量作用定律直接写出速率方程式率方程式(2)The rate equation of a non-elementary reaction depends on the results of experiment.对非元反应，速率方程式由实验测定对非元反应，速率方程式由实验测定N

15、2O5NO2O2(g)NO3NO2+(g)(g)N2O5(1)(2)(3)NO2+NO3+ NO2+ O2NO3+NONO2(overall reaction)(slow, rate-limiting step)(quick)(quick)52ONkcv Attention It is the sum of the exponents on the concentration terms in the rate equation.aA+bB=cC+dDyBxACkCv the order of reaction: n=(x+y)aA+bB=cC+dDIf it is a elementary

16、reaction:abABvkc cThe order of the reaction= a+b=molecularity of the reactionx=a；y=be.g：NO2+CO=CO2+NO (elementary reaction)2CONOvkccThe order of the reaction= 1+1=2=molecularity of the reactionReaction mechanism of CO+Cl2=COCl2 (phosgene)：(1)Cl22Cl（quick）212ClCl K 322Cl Cl ClK (2)Cl2+ Cl Cl3（quick）(

17、3)Cl3+COCOCl2+ Cl（slow，rate-limiting step）3ClCOvk cc322223ClCO32 ClClCO3232 Cl1 ClCOClCOvkcck K cc ck K cK cckcc32Cl2 ClClcK cc2Cl1 ClcK cThe overall reaction order is 1+3/2=2.5反应级数反应分子数使用范围任何反应 元反应 取值 整数、分数或负数 1，2，3与反应物系数和的关系不一定相等相等 dcdcvkckdtdtc 00ln ktcktcc ec或0lglg2.303ktcc A first-order reactio

18、n is one whose rate depends on the concentration of a single reactant raised to the first power dcdcvkckdtdtc 000ln r lgc- lgc2.303ktcktocc ecktDefinite integralY = mx + blgct0The curve of first-order reactionslope-2.303k(1)012012ln 12ln20.693 cktctkk021C is one whose rate depends on the reactant co

19、ncentration raised to the second power or on the concentrations of two different reactants each raised to the first power.反应速率与反应浓度的二次方成正比反应速率与反应浓度的二次方成正比22 dcdcvkckdtdtc Definite integral011 ktccY = mx + b二级反应方程式二级反应方程式1/ct0Slope=k 01InterceptcThe curve of second-order reaction(1)1201tkc The rate o

20、f reaction is independent on the concentration of the reactant.0 dcvkckdt Definite integralc = - kt +coY = mx + b零级反应方程零级反应方程式式ct0(1)Slope= - kThe curve of zero-order reaction0122ctk反应级数反应级数一级反应一级反应二级反应二级反应零级反应零级反应方程式方程式lgc =-kt/2.303 +lgc0 1/c = kt +1/c0c = -kt + c0 直线关系直线关系lgct1/ctct斜率斜率-k/2.303k-

21、kk单位单位s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kOrder First-Second-Zero-Equationlgc =-kt/2.303 + lgc01/c=kt+1/c0c=-kt+c0 Straightlinelgct1/ctctSlope-k/2.303k-kk (unit)s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kThe rate equation of the reaction:2N2O5NO2+O2 is listed below,25 N Ovkcaccording to25 N O

22、vkcThe reaction is a first-order reaction:02lg-2.3030.51.68 1060lg- 0.182mol/L2.303 cktccc-102.50.5mol L5c N2O5 remainsn(N2O5)=cV=0.1825=0.91molThe consumption of N2O5n(N2O5)=2.5-0.91=1.59molThere is a reaction :HbO2HbO2+in the blood of lung, it is first-order in Hb (hemoglobin) and also first-order

23、 in O2, the normal concentration of Hb and O2 are 8.010-6 molL-1 and 1.610-6 molL-1 respectively.at 37，k=2.1106mol-1L-1s-1(1) please calculate how quickly the HbO2 was created in the blood of lung(2) if suffering some kind of disease, V(HbO2)=1.110-4 molL-1s-1 in order to keep cHb unchanged,how much

24、 the c(O2) is in oxygen therapy. Because it is first order in Hb and also in O2It is known that the k of a reaction is 1.2410-4s-1, please calculate its half life. No matter the reaction is endothermic or exothermic, its rate increase with increasing temperature.aERTkAek is the rate constantEa is th

25、e activation energy R is the gas constant 8.314J/mol-KT is the absolute temperature.A:Called the frequency factorlnlnaEkART lglg2.303EakART21211 2lnrmkHTTkRTTuT2 T1 时时 k2 k1 ，反应速率，反应速率lglg2.303EakARTu当当T一定一定 时时,lgA一定一定,则则Ea愈大愈大, k愈小愈小，v愈慢愈慢u对不同的反应对不同的反应,温度对反应速率影响程度不温度对反应速率影响程度不同。当同。当T相同相同 时，时，Ea愈大，愈

26、大，斜率斜率Ea /T愈大愈大，k的的变化程度愈大变化程度愈大T/CT/Kk 10-51/T10-3lnk189.7462.92.522.160-10.589198.8418-9.855230.3503.56.301.986-7.370251.2507-5.757vant Hoff law：k (t+10)： rate constant at (t+10)kt： rate constant at t ：temperature coefficient.For a reaction , T, ； T , When the reactant is fixe

27、d, reaction rate increase 2 or 4 times with increasing temperature 10. 42k kt10t动能动能T T1 1T T2 2T T2 2 T T1 1()aNNEEaHigh temperatureLow temperatureMolecular kinetic energyFraction of molecules having a given kinetic energy Minimum energy needed for reaction,EaOrder First-Second-Zero-Equationlnc =-k

28、t + lnc01/c=kt+1/c0c=-kt+c0 Straightlinelnct1/ctctSlope-kk-kk (unit)s-1Lmol-1s-1molL-1s-1t1/20.693/k1/k c0c0/2kLower temperatureHigher temperatureKinetic energyMinimum energy needed for reaction,Ea EaEa加水溶解加水溶解NaCl物质以分子或离子为物质以分子或离子为单位互相混合，系统中单位互相混合，系统中没有界面，这类系统称没有界面，这类系统称为均相系统或均匀系统为均相系统或均匀系统如如NaCl溶液

29、溶液加水加水沙子沙子系统中有界面，界面两侧物质具有不系统中有界面，界面两侧物质具有不同的物理性质和化学性质同的物理性质和化学性质如泥浆、油水混合物等如泥浆、油水混合物等 A+C AC+B AB+C两反应途径活化能：两反应途径活化能：Ea1 Ea 、Ea2 Ea加入催化剂后，改变了化学反应途径，加入催化剂后，改变了化学反应途径，降低了活化能，反应速率得以提高降低了活化能，反应速率得以提高Ea2加入催化剂加入催化剂C后的反应途径后的反应途径：A + B ABEaEa1A + BABHEEE逆E逆途径途径1途径途径2BAcc 2kBACC 2kBAcc 2k2BckA + BABE2E1E1E2Ro

30、ute 1Route 2Ea1, Ea2 EaEa2In new route with catalyst C：A + B ABEaEa1 A+C AC+B AB+CThe activation energy of the reaction in new route is less than the activation energy of the reaction in original route, that increase the fraction of activated molecules in system, and increase the rate.（3）A catalyst

31、usually lowers the overall activation energy for a reaction by providing a completely different mechanism for the reactionH2O2(aq)2H2O+(l)Br-2(aq)+2H+Br2(aq)bromide ion2H2O2(aq)2H2O+ O2(l)(g)hydrogen peroxide+ O2(g)Br2(aq)+ H2O2(aq)Br-2(aq)+2H+bromineIn the absence of a catalyst this reaction occurs

32、 at an extremely slow rateA catalyst,bromide ion speeds the overall reaction without itself undergoing any net change.C2H4(g)+ H2(g)C2H6(g)ethyleneethaneThis reaction takes place very slowly under ordinary conditions. In the presence of a heavy metal such as nickel, palladium, or platinum, it occurs

33、 quickly at room temperature. The catalyzed reaction occurs at active sites on the surface of the solid. To maximize the surface area of the metal, it is used in the form of a fine powderlock-and-keyOdtdCvdtdCvCACA （2）the number of reaction rate of a reaction is connective with the change of the con

34、centration of the substance selected to express the reaction rate in a specific time interval. So we must give a clear indication of which substance was used to express the reaction rate.VA , VB , VC , VDtCtCCVIHHI2221加水溶解加水溶解NaCldissolvedNaClin water加水加水沙子沙子watersandHeterogeneous systemcollidingrea

35、ctionEffective collisioncollidingmove awayElastic collisionAABBAABBAABBReactants(initial state)Activated complex(transition state )Products(final state)Figure5-6 The activated complex物理论假设前题理论假设前题Hypothetical preconditions of the theoryCollision theory ：the molecule must have enough energy. The colliding molecules must have a favorable orientation. Transition state theory: (be similar with the above)The prerequisites of a reactionCollision theory ：the mol