Question

The rate law of the reaction 2H_2(g)+2NO(g)→N_2(g)+2H_2O(g) is rate=k[H_2[NO] ^2

Which of the following mechanisms cannot be possible?
a. 2NO⇌N 2O 2(fast equilibrium)
N_2 O_2 +H_2 →N _2O+H _2O (slow)
N_2 O +H_2 →N _2 +H _2O (fast)+
b. H_2+NO→H_2O+N (slow)
N+NO→N _2 +O (fast)
O+H_2→H_2O (fast)
c. H_2+2NO→N_2O+H_2OH_2(slow)
​N_2O+H _2→N_2+H 2_2 O (fast)
d. All three mechanisms are possible.

Answer 1

To determine which mechanism is not possible, we compare the proposed mechanisms with the given rate law. Mechanism a is not possible because it is not consistent with the rate law. Mechanisms b and c are possible because they are consistent with the rate law. Therefore, the correct answer is d, where all three mechanisms are possible.

Step-by-step explanation:

In order to determine which mechanism is not possible, we need to compare the proposed mechanisms with the given rate law. The rate law for the reaction is rate = k[H₂][NO]². Let's analyze each mechanism:

a. Mechanism: 2NO ⇌ N₂O₂ (fast equilibrium), N₂O₂ + H₂ → N₂O + H₂O (slow), N₂O + H₂ → N₂ + H₂O (fast)

Based on the proposed mechanism, the rate law for the slow step would be rate = k[N₂O₂] [H₂]. This is not consistent with the given rate law, so mechanism a is not possible.

b. Mechanism: H₂ + NO → H₂O + N (slow), N + NO → N₂ + O (fast), O + H₂ → H₂O (fast)

Based on the proposed mechanism, the rate law for the slow step would be rate = k[H₂] [NO]. This is consistent with the given rate law, so mechanism b is possible.

c. Mechanism: H₂ + 2NO → N₂O + H₂O, N₂O + H₂ → N₂ + H₂O (fast)

Based on the proposed mechanism, the rate law for the slow step would be rate = k[H₂] [NO]². This is consistent with the given rate law, so mechanism c is possible.

Therefore, mechanism d, where all three mechanisms are possible, is the correct answer.