For each of the reactions in parts (a), (b), and (c), suggest a mechanism and

apply the PSSH to learn if the mechanism is consistent with the rate law.

(a) The gas-phase homogeneous oxidation of nitrogen monoxide (NO) to

dioxide (N02),

2NO + 0 2 ~ 2N02

is known to have a form of third-order kinetics, which suggests that the

reaction is elementary as written, at least for low partial pressures of the

nitrogen oxides. However, the rate constant k actually decreases with

increasing absolute temperature, indicating an apparently negative activation

energy. Because the activation energy of any elementary reaction

must be positive, some explanation is in order.

Provide an explanation, starting from the fact that an active intermediate

species, N03 , is a participant in some other known reactions that involve

oxides of nitrogen. Draw the reaction pathway.