Reaction Mechanisms (College Board AP® Chemistry)

Nitrogen dioxide, NO₂(g) , is produced as a by-product of the combustion of fossil fuels in internal combustion engines. At elevated temperatures NO₂(g) decomposes according to the equation below.

2 NO₂(g)  →  2 NO(g) + O₂(g)

The concentration of a sample of NO₂(g) is monitored as it decomposes and is recorded on the graph directly below. The two graphs that follow it are derived from the original data.

Explain how the graphs indicate that the reaction is second order.

Write the rate law for the decomposition of NO₂(g) .

Consider two possible mechanisms for the decomposition reaction.

 i) Is the rate law described by mechanism I shown below consistent with the rate law you wrote in part (b) ? Justify your answer.

Mechanism I

 ii) Is the rate law described by mechanism II shown below consistent with the rate law you wrote in part (b) ? Justify your answer.

 Mechanism II