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:
$$\mathrm{CH}_{3} \mathrm{NC}(g) \longrightarrow \mathrm{CH}_{3}
\mathrm{CN}(g)$$
However, we also learned that gas-phase reactions occur through
collisions.
\begin{equation}
\begin{array}{l}{\text { a. One possible explanation is that two molecules of
} \mathrm{CH}_{3} \mathrm{NC} \text { collide }} \\ {\text { with each other
and form two molecules of the product in a single ele- }} \\ {\text { mentary
step. If that is the case, what reaction order would you expect? }}\\\\{\text
{ b. Another possibility is that the reaction occurs through more than }} \\\
{\text { one step. For example, a possible mechanism involves one step in }}
\\\ {\text { which the two CH}_{3} \mathrm{NC} \text { molecules collide,
resulting in the activation" }} \\ {\text { of one of them. In a second step,
the activated molecule goes on to }}\\\\{l}{\text { form the product. Write
down this mechanism and determine which }} \\ {\text { step must be rate
determining in order for the kinetics of the reaction }} \\ {\text { to be
first order. Show explicitly how the mechanism predicts first- }} \\ {\text {
order kinetics. }}\end{array}
\end{equation}
