The reaction of NO2 (g) and CO (g) is thought to occur in two steps:

Step1 Slow NO2 (g) + NO2 (g) ---> NO (g) + NO3 (g)
Step2 Fast NO3 (g) + CO (g) ---> NO2 (g) + CO2 (g)

a. Show that the elementary steps add up to give the overall, stoichiometric equation.
b. What is the molecularity of each step?
c. For this mechanism to be consistent with kinetic data, what must be the
experimental rate equation?
d. Identify any intermediates in this reaction.

Overall equation:

a)CO(g) + NO2(g) → CO2(g) + NO(g)

b)Each step is bimolecular

c)Rate=k[NO2]^2

d)NO3 is an intermediate

Explanation:

To obtain the overall rate equation we cancel out reactants and products that are the same on both sides of the both steps. This leaves us with CO(g) + NO2(g) → CO2(g) + NO(g) as the overall stoichiometric reaction equation. Each step involves the reaction of two molecules hence each step in the mechanism is bimolecular. The slow step involves the reaction of NO2 hence the rate of reaction depends on the first step of the reaction hence the rate equation shown in the answer. Intermediates only take part in elementary steps but do not appear as products or reactants. They are produced and consumed transiently. NO3 is an intermediate in this reaction.