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1、Chapter 26Chapter 26 The Kinetics of complex ReactionsThe Kinetics of complex ReactionsChain reactionsChain reactions polymerizationpolymerizationHomogeneous catalysisHomogeneous catalysisChapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics2 2explosiveexplosiveEnzym
2、e-catalyzedEnzyme-catalyzedOscillation reactionsOscillation reactionsautocatalysisautocatalysisphotochemistryphotochemistry26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactions Consider the thermal decomposition of Consider the thermal decomposition of acetaldehyde acetaldehyde
3、CHCH3 3CHO(g) CHO(g) CHCH4 4(g)+ CO(g) (g)+ CO(g) v v = = k kCHCH3 3CHOCHO3/23/2Three steps:1. 1. Initiation: CHInitiation: CH3 3CHOCHO CHCH3 3+ + CHO CHO v v = = k ki iCHCH3 3CHOCHO2. 2. Propagation: CHPropagation: CH3 3CHO+ CHO+ CHCH3 3CHCH4 4+ CH + CH3 3COCO k kp pPropagation: CHPropagation: CH3
4、3COCO CHCH3 3+ CO + CO kkp p3. 3. Termination: Termination: CHCH3 3+ + CHCH3 3 CH CH3 3CHCH3 3 k kt t3 3Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactions The net rates of change of the inte
5、rmediates are: The net rates of change of the intermediates are:4 4Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics Applying the steady state approximation: Applying the steady state approximation:26.1 26.1 The rate laws of chain reactionsThe rate laws of chain
6、reactions Sum of the above two equations equals: Sum of the above two equations equals:5 5Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics The rate of formation of CH The rate of formation of CH4 4can be expressed as can be expressed as thus the steady state con
7、centration of thus the steady state concentration of CH3 is:CH3 is:26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactions Example: The hydrogen-bromine reaction has Example: The hydrogen-bromine reaction has complicated rate law rather than the second order complicated rate law r
8、ather than the second order reaction as anticipated. reaction as anticipated. 6 6Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kineticsH2(g) + Br2(g) 2HBr(g)26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactionsThe following mechanism has been prop
9、osed The following mechanism has been proposed to account for the above rate law.to account for the above rate law.7 7Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics1. 1. Initiation: BrInitiation: Br2 2+ M Br + M Br + Br + Br + M + Mk ki i2. Propagation: Br + H
10、2 HBr + H kp1H H + Br + Br2 2 HBr HBr + Br+ Br k kp2p23. 3. Retardation: Retardation: H H + + HBr HBr H H2 2+ Br + Br k kr r4. 4. Termination: BrTermination: Br + Br + Br + M Br + M Br2 2+ M* + M* k kt tderive the rate law based on the above mechanism.derive the rate law based on the above mechanism
11、.26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactions The The net net rates rates of of formation formation of of the the two two intermediates areintermediates are8 8Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics26.1 26.1 The rate laws o
12、f chain reactionsThe rate laws of chain reactions The The steady-state steady-state concentrations concentrations of of the the above above two two intermediates intermediates can can be be obtained obtained by by solving solving the the following two equations:following two equations:9 9Chapter 26
13、The kinetics of complex kineticsChapter 26 The kinetics of complex kinetics26.1 26.1 The rate laws of chain reactionsThe rate laws of chain reactions Substitute Substitute the the above above results results to to the the rate rate law law of of HBrHBr 1010Chapter 26 The kinetics of complex kinetics
14、Chapter 26 The kinetics of complex kinetics The The above above results results has has the the same same form form as as the the empirical empirical rate rate law, and the two empirical rate constants can be identified aslaw, and the two empirical rate constants can be identified as26.2 26.2 Explos
15、ionsExplosions A A thermal thermal explosionexplosion is is a a very very rapid rapid reaction reaction arising arising from from a a rapid rapid increase increase of of reaction reaction rate rate with with increasing temperature.increasing temperature.1111Chapter 26 The kinetics of complex kineticsChapter 26 The kinetics of complex kineticsA chain-branching chain-branching explosionexplosion occurs when the number of cha
