Question

Nitric oxide reacts with hydrogen to give nitrogen and water.

\[\ce{2NO + 2H2 -> N2 + 2H2O}\]

The kinetics of this reaction is explained by the following steps:

1. \[\ce{2NO + H2 -> N2 + H2O2}\] (slow)
2. \[\ce{H2O2 + H2 -> 2H2O}\]

What is the predicted rate law?

Answer 1

Given overall reaction:

\[\ce{2NO + 2H2 -> N2 + 2H2O}\]

Proposed mechanism:

Step 1 (Slow-rate-determining):

\[\ce{2NO + H2 −> N2 + H2O2}\]

Step 2 (Fast):

\[\ce{H2O2 + H2 −> 2H2O}\]

Since the rate-determining step is the first (slow) step, the rate law is based on that step.

From step 1:

Rate = k[NO]²[H₂]

This rate law is consistent with the mechanism, as the slow step involves two NO molecules and one H₂ molecule.