【精品】Reaction Kinetics 86.ppt
1,Reaction Kinetics(1),Xuan ChengXiamen University,Physical Chemistry,2,Physical Chemistry,Reaction Kinetics,For example,-16.63,-237.19,Thermodynamics:spontaneous reactions(possible to take place),Thermodynamics:cant answer(1)how to make them happen(2)how fast they will take place(3)the reaction mechanism,Reaction Kinetics,3,Physical Chemistry,Reaction Kinetics,T,P,catalyst,T,catalyst,Chemical Kinetics:,Chemical Kinetics,The study of the rates and mechanisms of chemical reactions,A reacting system is not in equilibrium,Reaction Kinetics,4,Physical Chemistry,Rate of Reaction,Consider the homogeneous reaction(occurs entirely in one phase),(17.1),The rate of conversion J,(17.2),At equilibrium,J=0,Reaction Kinetics,5,Physical Chemistry,Rate of Reaction,(17.3),(17.4)*,At constant V,The rate of reaction r,mol dm-3 s-1,mol cm-3 s-1,Reaction Kinetics,6,Physical Chemistry,Rate Laws,For many reactions,(17.5)*,k:rate constant(rate coefficient),k=f(T,P),:order or partial order,+n:overall order,The expression for r as a function of concentrations at a fixed temperature is called the rate law.,Reaction Kinetics,7,Physical Chemistry,Reaction Orders,Zero-order,First-order,Second-order,Third-order,Negative First-order,1.5-order,No simple order,Reaction Kinetics,8,Physical Chemistry,Rate Laws,Reaction,Rate Law,Reaction Kinetics,9,Physical Chemistry,Reaction Mechanisms,(17.7),intermediate,(17.8),Step(a),Step(b),Step(c),Elementary reaction,Reaction actually occurs,Reaction Kinetics,10,Physical Chemistry,Measurement of Reaction Rates,Chemical Method,The concentration of a reactant or product as a function of time,Reaction vessels,At constant T,At intervals,Slows down or stop the reaction,Rapidly analyze chemical compositions of the mixture,Reaction Kinetics,11,Physical 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 Kinetics,12,Physical Chemistry,Measurement of Reaction Rates,Physical Method,Measures 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，从而求得浓度变化。物理方法有可能做原位反应。,Reaction Kinetics,13,Physical Chemistry,Integration of Rate Laws,Assumptions,(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),(17.4)*,Integrate it to find A as a function of time:A=g(t),Reaction Kinetics,14,Physical Chemistry,First-Order Reactions,(17.4)*,(17.5)*,(17.10),define,(17.11),Reaction Kinetics,15,Physical Chemistry,First-Order Reactions,(17.12),(17.13),(17.14)*,The concentration of A(and r)decreases exponentially with time for a first-order reaction.,(17.10),Integrated rate law,Reaction Kinetics,16,First-order reaction:lnA vs t,First-Order Reactions,Physical Chemistry,(17.14)*,First-order reaction:A/Ao vs t,Reaction Kinetics,17,First-Order Reactions,Physical Chemistry,Half-life:,(17.13),The time needed for A to drop to half its value,Independent of Ao,A useful indication for the chemical reaction rate,Reaction Kinetics,18,Second-Order Reactions,Physical Chemistry,(17.10),Reaction Kinetics,19,Second-Order Reactions,Physical Chemistry,(17.16),A plot of 1/A versus t gives a strait line of slope kA if,(17.17),Reaction Kinetics,20,Second-Order Reactions,Physical Chemistry,(17.16),Half-life:,Second-order reaction with r=kA2,Reaction Kinetics,21,Second-Order Reactions,Physical Chemistry,Second-order reaction with r=kA2,First-order reaction with r=kA,(17.18),Three variables,Reaction Kinetics,22,Second-Order Reactions,Physical Chemistry,x=0 when t=0,Reaction Kinetics,23,Second-Order Reactions,Physical Chemistry,(17.22),Reaction Kinetics,24,Second-Order Reactions,Physical Chemistry,If Ao=Bo,(17.23),Half-life:,Reaction Kinetics,25,Third-Order Reactions,Physical Chemistry,(Problems 17.17 and 17.24),(17.24),Reaction Kinetics,26,nth-Order Reaction,Physical Chemistry,Consider,(17.25),Integration gives,(17.26),Reaction Kinetics,27,nth-Order Reaction,Physical Chemistry,For n=1,(17.30),Half-life:,(17.26),For n=0,Reaction Kinetics,28,Homework,Physical Chemistry,Page 591,Prob.17.5,Prob.17.6,Prob.17.8,Prob.17.10,Reaction Kinetics,29,
