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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

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

slide2

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
slide3

Chemical Reactions

1. Zero-order reactions

2. First-order reactions

slide4

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.

slide5

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

chemical reaction
Chemical Reaction

4. n-th Order

[Except first order]

[Except first order]

2 4 use of physical properties with kinetic data
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

2 5 methods when the infinity reading end point is unknown
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.

2 8 the experimental determination of reaction orders
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}

2 9 reactions with a complex dependence on a single concentration variable
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

slide11

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.