Question

What is the rate of reaction and the order of reaction if the mechanism of the reaction is

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

\[\ce{H2O2 + H2 -> 2H2O}\] (fast)

Answer 1

Given mechanism:

Step 1 (Slow – Rate-Determining Step):

\[\ce{2NO + H2 -> N2 + H2O2}\]

Step 2 (Fast):

\[\ce{H2O2 + H2 −> 2H2O}\]

Since the rate of a reaction is determined by the slowest step, the rate law is based on Step 1 only.

Rate = k[NO]²[H₂]

Because:

Two molecules of NO are involved → order with respect to NO = 2

One molecule of H₂ is involved → order with respect to H₂ = 1

∴ Overall order = 2 + 1 = 3

∴ The rate of reaction is Rate = k[NO]²[H₂] and order of reaction is 3.