Consider the following reaction.

\[2{\text{NO(g)}} + 2{{\text{H}}_2}({\text{g)}} \to {{\text{N}}_2}({\text{g)}} + 2{{\text{H}}_2}{\text{O(g)}}\]

A proposed reaction mechanism is:

\[\begin{array}{*{20}{l}} {{\text{NO(g)}} + {\text{NO(g)}} \rightleftharpoons {{\text{N}}_2}{{\text{O}}_2}{\text{(g)}}}&{fast} \\ {{{\text{N}}_2}{{\text{O}}_2}{\text{(g)}} + {{\text{H}}_2}{\text{(g)}} \to {{\text{N}}_2}{\text{O(g)}} + {{\text{H}}_2}{\text{O(g)}}}&{slow} \\ {{{\text{N}}_2}{\text{O(g)}} + {{\text{H}}_2}{\text{(g)}} \to {{\text{N}}_2}{\text{(g)}} + {{\text{H}}_2}{\text{O(g)}}}&{fast} \end{array}\]

What is the rate expression?

A.     \({\text{rate}} = k{\text{[}}{{\text{H}}_2}]{[{\text{NO]}}^2}\)

B.     \({\text{rate}} = k{\text{[}}{{\text{N}}_2}{{\text{O}}_2}][{{\text{H}}_2}]\)

C.     \({\text{rate}} = k{{\text{[NO]}}^2}{[{{\text{H}}_2}]^2}\)

D.     \({\text{rate}} = k{{\text{[NO]}}^2}{[{{\text{N}}_2}{{\text{O}}_2}]^2}[{{\text{H}}_2}]\)

A

There were three G2 comments on this question. Two of these comments stated the question was very difficult and one comment stated that the first step should have had an equilibrium sign which is correct. The question itself was answered correctly by only 46.28% and was the third most difficult question on the entire paper.