89.2 Reaction rate and rate equation I.R. Levine, pp 528-533 17.1 reaction kinetics 17.2 measurement of reaction rates
§9.2 Reaction rate and rate equation I. R. Levine, pp. 528-533 17.1 reaction kinetics; 17.2 measurement of reaction rates
89.2 Reaction rate and rate equation (1) Expression of reaction rate The rate (r of a chemical reaction is defined as the concentration change of a reactant or a product per unit time A mean rate △A]c2-C1 instantaneous rate: r △t Physical meaning Initial instantaneous rate?
The rate (r) of a chemical reaction is defined as the concentration change of a reactant or a product per unit time. (1) Expression of reaction rate instantaneous rate: d[A] r dt = t1 t c 2 1 2 1 [A] = c c r t t t − = − mean rate t c t1 t2 c1 c2 Physical meaning: Initial instantaneous rate? §9.2 Reaction rate and rate equation
89.2 Reaction rate and rate equation (1) Expression of reaction rate N,+3H,==2NH dc dt It is apparent that NH When expressed using different species, the rate of the reaction may attain different values, which is not convenient and sometimes may even cause confusion
N2 + 3H2 == 2NH3 2 2 H H dc r dt = − 2 2 N N dc r dt = − 3 3 NH NH dc r dt = It is apparent that N H NH 2 2 3 1 1 3 2 r r r = = When expressed using different species, the rate of the reaction may attain different values, which is not convenient and sometimes may even cause confusion. (1) Expression of reaction rate §9.2 Reaction rate and rate equation
89.2 Reaction rate and rate equation (1) Expression of reaction rate Definition Definition extent of reaction or advancement(5) The true rate of the reaction or rate of conversion ( dt where v is the stoichiometric coefficient of the reaction What is its Unit? +3H2==2NH3 aA+bB→gG+hH
Definition: extent of reaction or advancement () i i,0 i n n − = where i is the stoichiometric coefficient of the reaction. Definition: The true rate of the reaction or rate of conversion (J): dt d J = aA + bB → gG + hH What is its Unit? (1) Expression of reaction rate §9.2 Reaction rate and rate equation N2 + 3H2 == 2NH3
89.2 Reaction rate and rate equation (1) Expression of reaction rate When the reaction takes place in a container For general reaction: with constant volume or in solution without aA+bB→gG+hH change of solution volume When the extent ofreaction is ds Define rate dh l5 h d[a l d[a 1 dg] 1 d[hi J=2=- dna=- 1 dng- 1 dnu r= a dt b dt g dt h dt g I d cl n olm- s
For general reaction: aA + bB → gG + hH When the extent of reaction is d A B H G dn dn dn dn d a b g h = − = − = = 1 1 1 1 A B H G d dn dn dn dn J dt a dt b dt g dt h dt = = − = − = = When the reaction takes place in a container with constant volume or in solution without change of solution volume Define rate V J r = (1) Expression of reaction rate §9.2 Reaction rate and rate equation dt d dt h d dt g d dt b d a r 1 [A] 1 [A] 1 [G] 1 [H] = − = − = = dt d c r i i 1 [ ] = Unit: mol m-3 s -1