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
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.