89.2 Reaction rate and rate equation (5) The law of mass action Exercise For elementary reaction such as 21+H2=2HI k 2 at k[][H 2A B +C E Partial order= stoichiometric coefficient daI db dc dd de Reaction order= number of molecules involved in the reaction Law of mass action valid only for elementary reactionFor elementary reaction such as A A B C dc a b c r kc c c dt    Partial order = stoichiometric coefficient Reaction order = number of molecules involved in the reaction 2I + H2 = 2HI 2 2 1 [I] [I] [H ] 2 d r k dt    Law of mass action valid only for elementary reaction (5) The law of mass action §9.2 Reaction rate and rate equation 2A k1 k2 B + C D E k3 k4 dt d[A] dt d[B] dt d[C] dt d[D] dt d[E] Exercise