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Lecture_09_Kinetics - Kinetics IV Chemical Reaction...

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Seoul National University Solid State Ionics Research Lab. Kinetics IV. Chemical Reaction Kinetics
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Seoul National University Solid State Ionics Research Lab. Kinetics 0. Reaction systems to discuss: - Closed, constant-volume : Easier to treat theoretically and experimentally - Isothermal : For a very rapid reaction, it maybe easier to treat as an adiabatic system - Homogeneous in terms of reaction sites : Homogeneous reaction proceeds ; Heterogeneous reaction sites may be excluded for the sake for simplicity Lect.#9 (10/30/07; 100 min)
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Seoul National University Solid State Ionics Research Lab. Kinetics 1. Chemical Reaction Rate and Rate Laws -In a closed constant-volume system, the rate of a chemical reaction can be defined simply as the rate of change with time of the concentration of any of the reactants or products. d[A] d[B] d[C] d[D] (Rate R); - , - , , dt dt dt dt [ ] : concentration in arbitrary units A,B,C,D: reacting species a,b,c,d: stoichiometric coefficients +ve constant -For the rate to be independent of components, in terms of extent of rxn : [ ] 1 [ ] 1 [ ] 1 [ ] 1 [ ] 1 i i d A d A d B d C d D d R a dt b dt c dt d dt dt dt     aA+bB cC+dD or 0= i i i A 1.1 Definition of the reaction rate
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Seoul National University Solid State Ionics Research Lab. Kinetics 1.2 Concentration change in general -If the constant-volume condition is removed; 3 causes for conc. change diffusion(D) volume change(V) chemical reaction (R) VD VR RD C C C dC dt dt dV t t V Volume change (V) Diffusion (D) Chemical rxn (R)
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Seoul National University Solid State Ionics Research Lab. Kinetics 2 / 1 C n V dC dn n dV dt V dt V dt VD C R t ( ) VR C D C t   2 RD C n n V V V V   1 ( ) if dV=0 dn R D C V dt     -Only in the case of a constant-volume system with no diffusion ; 1 dn dc R V dt dt (reaction) (diffusion) (volume change)
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Seoul National University Solid State Ionics Research Lab. Kinetics - In general the reaction rate can be a function of all the species present in a reaction mixture. -The rate law for a given reaction 1/2 2 2 ' 2 [ ][ ] 1 [ ] 2 1 [ ]/[ ] k H Br d R HBr dt k HBr Br e.g.) 1 2 ( , , , ) j R f c c c -The form of the rate law is determined by experiment, and canno predicted from the stoichiometric coefficients for the overall reaction. 2 2 2 H Br HBr 1.3 Reaction rate
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Seoul National University Solid State Ionics Research Lab. Kinetics -In many cases, 1 2 1 2 1 2 ( , , ) j n n n j R f c c kc c c ; overall reaction order j j n n j n k ; partial reaction order, the reaction order with respect to the component j (may not be an integer) ; rate constant or specific rate Note : dimension of k
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Seoul National University Solid State Ionics Research Lab.
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