A proposed mechanism for the reaction 2 NO(g) + 2 H₂(g) $\to$ N₂(g) + 2 H₂O(g) is Step 1: 2 NO(g) $\to$ N₂O₂(g)
(very fast,reversible)
Step 2: N₂O₂(g) + H₂(g) $\to$ N₂O(g) + H₂O(g) (slow)
Step 3: N₂O(g) + H₂(g) $\to$ N₂(g) + H₂O(g) (fast)
What is the rate law for the overall reaction?

Question

A proposed mechanism for the reaction 2 NO(g) + 2 H₂(g)

\to

N₂(g) + 2 H₂O(g) is Step 1: 2 NO(g)

\to

N₂O₂(g)
(very fast,reversible)
Step 2: N₂O₂(g) + H₂(g)

\to

N₂O(g) + H₂O(g) (slow)
Step 3: N₂O(g) + H₂(g)

\to

N₂(g) + H₂O(g) (fast)
What is the rate law for the overall reaction?

Quizplus · Accepted Answer

The rate-determining step is the slow step, which involves the N₂O and H₂ reaction. The rate law for the slow step can be written as rate = k[N₂O][H₂]. Since the first step is fast and reversible, it does not affect the overall rate law. Therefore, the rate law for the overall reaction can be written as rate = k[NO]²[H₂] (from the second and third steps) or rate = k[NO]²[N₂O][H₂] (combining the rate laws from the slow step and the first step). The only choice that matches this is E.

A Proposed Mechanism for the Reaction 2 NO(g)+ 2 H2(g) →\to→

A Proposed Mechanism for the Reaction 2 NO(g)+ 2 H₂(g) $\to$