Problem 12-79

Mechanism:

You need first the order of the reaction of problem 39 by the method of initial rate:

2NO(g) + Cl₂ → 2NOCl

Once the order of [NO] and [Cl₂] is known, check whether the first elementary step is identical to that of problem 39.
If so, the first reaction is the rate determining step. Otherwise, it is the second elementary step.