Question

The following mechanism has been proposed for the reaction of NO with H₂ to form N₂O and H₂O:

Step 1: NO(g) + NO(g) → N₂O₂(g)
Step 2: N₂O₂(g) + H₂(g) → N₂O(g) + H₂O(g)

What is the rate law for each elementary step?

Answer 1

The rate law for Step 1 of the mechanism is rate = k1[NO]2 and for Step 2 is rate = k2[N2O2][H2]. If Step 2 is the rate determining step, then the concentration of N2O2 is substituted in terms of [NO] and [H2], leading to the experimentally determined overall rate law matching the mechanism.

Step-by-step explanation:

The mechanism proposed for the reaction of nitrogen monoxide (NO) with hydrogen (H₂) to form nitrous oxide (N₂O) and water (H₂O) consists of two elementary steps:

• Step 1: NO(g) + NO(g) → N₂O₂(g)
• Step 2: N₂O₂(g) + H₂(g) → N₂O(g) + H₂O(g)

The rate law for each elementary step is derived from the molecularity of the reaction:

• The rate law for Step 1, which involves a bimolecular collision between two NO molecules, is rate = k1[NO]2.
• The rate law for Step 2, which is a bimolecular reaction between N₂O₂ and H₂, is rate = k2[N₂O₂][H₂].

Overall, the mechanism must correlate with the experimentally determined rate law for the reaction, which is rate = k[NO]2[H₂]. If Step 2 is the rate determining step, then the concentration of N₂O₂ can be expressed in terms of the concentrations of NO and H₂, resulting in the observed rate law.