Chapter 14, Problem 118AP

At a certain elevated temperature, ammonia decomposes on the surface of tungsten metal as follows:

${\text{2NH}}_{\text{3}}\underset{}{\to }{\text{ N}}_{\text{2}}{\text{+ 3H}}_{\text{2}}$

From the following plot of the rate of the reaction versus the pressure of ${\text{NH}}_{\text{3}}$, describe the mechanism of the reaction.