Question

Nitrogen monoxide, NO, reacts with hydrogen, H2, according to the following equation. 2 NO + 2 H2 → N2 + 2 H2O What would the rate law be if the mechanism for this reaction were as follows? (Rate expressions take the general form: rate = k . [A]a . [B]b.) 2 NO + H2 → N2 + H2O2 (slow) H2O2 + H2 → 2 H2O (fast)

Answer 1

Answer: The rate law for the reaction is $\text{Rate}=k[NO]^2[H_2]$

Explanation:

In a mechanism of the reaction, the slow step in the mechanism determines the rate of the reaction.

For the given chemical reaction:

$2NO+2H_2(g)\rightarrow N_2+2H_2O$

The intermediate reaction of the mechanism follows:

Step 1:  $2NO+H_2\rightleftharpoons N_2+H_2O_2;\text{ (slow)}$

Step 2:  $H_2O_2+H_2\rightarrow 2H_2O;\text{(fast)}$

As, step 1 is the slow step. It is the rate determining step

Rate law for the reaction follows:

$\text{Rate}=k[NO]^2[H_2]$

Hence, the rate law for the reaction is $\text{Rate}=k[NO]^2[H_2]$