89.5 Temperature-dependence of reaction rate Arrhenius equation Extensive reading: Levine, pp. 554-559 Section 17.8 oals 1. Describe the effect of temperature on reaction rate 2. Activation energy: definition, measurement, estimation 3. Fundamentals for higher level scientific researches
§9.5 Temperature-dependence of reaction rate -- Arrhenius equation Extensive reading: Levine, pp. 554-559 Section 17.8 Goals: 1. Describe the effect of temperature on reaction rate; 2. Activation energy: definition, measurement, estimation; 3. Fundamentals for higher level scientific researches
89.5 Arrhenius equation qualitative Semi-quantitative quantitative dInk A T+10 2~3 +B kr nK)_△ dInk e aT RT Simplification dT RT
§9.5 Arrhenius equation qualitative Semi-quantitative quantitative 10 2 ~ 3 T T k k + = 2 ln A B d k dT T = + 2 ln r m p K H T RT = Simplification 2 d ln d E a k T RT =
89.5 Arrhenius equation △U=E.-E a.+ E=E-E E=E-E a Arrhenius Tolman a:4 E E E
U = Ea,+ − Ea,− §9.5 Arrhenius equation Ea = E − E * Ea = E − E * Tolman Arrhenius Ea,1 Ea,2 Ea,3 Ea,4 Ea,5 Ea,6
89.5 Arrhenius equation 9.5.11 modification of Arrhenius equation 3参数拟合 The Arrhenius plots for some reactions are curved, which suggests that the activation energy of these reactions is a function of temperature. At this situation, the temperature dependence of k can be usually expressed as 2参数拟合 k=AT expl E RT 1.0 20 3.0 4.0 5.0 1000 / E k= Aexp Problem: RT Discussion the relationship dInkA between this equation and tB Deduce the relationship between ea and e vant' Hoff empirical equation
9.5.11 modification of Arrhenius equation The Arrhenius plots for some reactions are curved, which suggests that the activation energy of these reactions is a function of temperature. At this situation, the temperature dependence of k can be usually expressed as: = − RT E k AT m c exp 2 ln B d k A dT T = + Problem: Discussion the relationship between this equation and vant’ Hoff empirical equation Deduce the relationship between Ea and Ec . exp E c k A RT = − §9.5 Arrhenius equation
89.5 Arrhenius equation 9.5.11 modification of Arrhenius equation E=mRT+e However for some reaction such as rT 2 44 kJ mol-I CCl3 COOH>CHCI3+CO2, m=-107 m, usually be 0, 1, 2, 1/2,etc,is CH, Br +ho>CHoh +H++ Br very large m=-34.3 In a relatively small temperature The effect of temperature on the activation range, Ea seems independent on energy of these reactions is too large to ignore temperature Temperature-dependence of e
m, usually be 0, 1, 2, 1/2, etc., is not very large. In a relatively small temperature range, Ea seems independent on temperature. Ea = mRT + Ec However, for some reaction such as: CCl3COOH → CHCl3 + CO2 , m = -10.7 CH3Br + H2O → CH3OH + H+ + Br− , m = -34.3 The effect of temperature on the activation energy of these reactions is too large to ignore. Temperature-dependence of Ea RT= 2.44 kJ mol-1 9.5.11 modification of Arrhenius equation §9.5 Arrhenius equation