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J. W. Hill, R. H. Petrucci, T. W. McCreary, & S. S. Perry General Chemistry, 4th edition.

Problem 13.61.

The following is proposed as a plausible reaction mechanism:
A + B I (slow)
I + B C + D (fast)

What is (a) the net reaction described by this mechanism and (b) a plausible rate law for the reaction?




Answer:

(a) To find the net reaction, sum up all the reactions in the mechanism and eliminate common species on each side of the equation:

A + B + I + B I + C + D

net: A + 2B C + D

(b) The rate law is determined by the slow step in the reaction mechanism. Since a reaction mechanism is composed of elementary reactions, the rate law for the slow step can be written by inspection, with the orders of reaction being the stoichiometric coefficients:

Rate = k[A][B]