A. The gas-phase homogeneous oxidation of nitrogen monoxide (NO) to dioxide (NO2),
2NO + O2→ 2NO2

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, NO3, is a participant in some other known reactions that involve oxides of nitrogen. Draw the reaction pathway.

b. The rate law for formation of phosgene, COC12, from chlorine, C12, and carbon monoxide, CO, has the rate law.

rCOCl2= k Cco C3/2. Cl2

Suggest a mechanism for this reaction that is consistent with this rate law and draw the reaction pathway. (Hint: Cl formed from the dissociation of C12 is one of the two active intermediates.)
c. List ways you can work this problem incorrectly.
d. How could you make this problem more difficult?