In this chapter, we have seen a number of reactions in which a single reactant forms products. For example, consider the following first-order reaction:

CH₃NC(g) → CH₃CN( g)

However, we also learned that gas-phase reactions occur through collisions.

a. One possible explanation for how this reaction occurs is that two molecules of CH₃NC collide with each other and form two molecules of the product in a single elementary step. If that were the case, what reaction order would you expect?

b. Another possibility is that the reaction occurs through more than one step. For example, a possible mechanism involves one step in which the two CH₃NC molecules collide, resulting in the “activation” of one of them. In a second step, the activated molecule goes on to form the product. Write down this mechanism and determine which step must be rate determining in order for the kinetics of the reaction to be first order. Show explicitly how the mechanism predicts first-order kinetics.