Question

A possible mechanism for the reaction of carbon monoxide with nitrogen dioxide is:

$2{NO}_2\left(g\right)\to {NO}_3\left(g\right)+NO\left(g\right)$ (slow)

${NO}_3\left(g\right)+CO\left(g\right)\to {NO}_2\left(g\right)+{CO}_2\left(g\right)$ (fast)

Which of the following could be the rate law for this reaction?

• A. Rate = $k\left[{NO}_2\right]$
• B. Rate = ${k\left[{NO}_2\right]}^2$
• C. Rate = $k\left[{NO}_3\right]\left[CO\right]$
• D. Rate = $k\left[{NO}_3\right]\left[CO\right]{\left[{NO}_2\right]}^2$
• E. Rate = $k\left[NO\right]\left[{NO}_3\right]/{\left[{NO}_2\right]}^2$

Answer 1

The correct option is B Rate = ${k\left[{NO}_2\right]}^2$

A rate of a reaction is determined from the slowest step of the reaction. In the above question, the first equation is the slowest step, hence the rate should be determined to form this step. The reactant has 2 moles of Nitrogen dioxide.

Hence, the rate of the reaction is given by $k$$[N{O}_2{]}^2$, where k is the rate constant.