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Chapter 2

Chemical Kinetics and Reaction Mechanisms. Chapter 2. Reactions with a Simple Kinetic Form. Prof. Kyoung -Ho Park. Prepared from Chemical Kinetics and Mechanism, 2 nd Ed. James H. Espenson. 1 . Zero-order reactions 2 . First-order reactions 3 . Second-order reactions

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Chapter 2

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  1. Chemical Kinetics and Reaction Mechanisms Chapter 2 Reactions with a Simple Kinetic Form Prof. Kyoung-Ho Park Prepared from Chemical Kinetics and Mechanism, 2nd Ed. James H. Espenson

  2. 1. Zero-order reactions • 2. First-order reactions • 3. Second-order reactions • 3-1 Pseudo first order reactions • 4. Summary for reaction orders 0, 1, 2 and n • Equilibrium reactions or opposed reactions

  3. Chemical Reactions 1. Zero-order reactions 2. First-order reactions

  4. An example of first-order kinetics is the hydrolysis of triphenylmethyl chloride, Ph3CCl + H2O = Ph3COH + H+ + Cl- (2-10) Sample data are given in Table 2-1. Calculate k (rate constant) using the least-square method.

  5. Chemical Reactions 3-1 Pseudo first order reac. where k' = k[B]0 (k' or kobswith units s-1) and we have an expression identical to the first order expression above. 3. Second-order reactions

  6. Chemical Reaction 4. n-th Order [Except first order] [Except first order]

  7. 2.4 Use of physical properties with kinetic data • For first-order kinetics; ln {[A]t/[A]o} = ln {(Yt - Y∞)/(Yo– Y∞)} = - kt ln {(Yt - Y∞)/(Yo– Y∞)} = - kt

  8. 2.5 Methods when the infinity reading (“end point”) is unknown • Guggenheim plot; ln {(Yt- Yt+τ)/(Yo– Y∞)} = - kt, ln (Yt- Yt+τ) = - kt + constants ※τis chosen as two to three half-times.

  9. 2.8 The experimental determination of reaction orders ◈ Determinated and Integrated rate law; dx/dt = v = k[A]n → ln v = n ln [A] + ln k ◈ half-life method; ln t1/2 = ln (2n-1– 1) – ln {(n-1)k[Ao]n-1} ln t1/2 = -(n-1)ln [Ao] + ln {(2n-1– 1)/k}

  10. 2.9 Reactions with a complex dependence on a single concentration variable • Concurrent first-order and second-order kinetics is found in several circumstances. 1) V = k1[A] + 2k2[A]2 ; The case when A is a free radical that can both dimerize (v2 = 2k2 [A] 2) and react with a substrate (v1=k1 [A][S], with [S]o>>[A]o). ※ Show in section 3.5

  11. V = k[A]/(κ +[A]); This is the rate law for many catalyzed reactions, including those catalyzed enzymers. • V = k1[A]/{1+(1+k2[A]1/2}; This peculiar form applies when a dimeric molecule dissociates to a reactive monomer that then undergoes a first-order or pseudo-first order reaction.

  12. 2.10 Product-catalyzed reactions

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