Question

Given the following proposed mechanism, predict the rate law for the overall reaction.

2NO₂ + Cl₂→ 2NO₂CI (overall reaction)
Mechanism
NO₂ + Cl₂→ NO₂CI+ CI slow NO₂CINO₂CI fast
a. Rate = k(NO₂CI][CI]²
b. Rate = k[NO₂][CI]²
c. Rate = k(NO₂CI]²
d. Rate = k[NO₂]2[CI₂]
e. Rate = k[NO₂][C₂]

Answer 1

The rate law for the overall reaction 2NO2 + Cl2 → 2NO2Cl, given the slow first step, is rate = k[NO2][Cl2].

Step-by-step explanation:

To predict the rate law for the overall reaction 2NO2 + Cl2 → 2NO2Cl, we consider the proposed mechanism and the slowest step, which is the rate-determining step. Given the mechanism:

• Step 1: NO2 + Cl2 → NO2Cl + Cl (slow)
• Step 2: NO2Cl + NO2 → 2NO2Cl (fast)

Since step 1 is the slow step, the rate law is given by the rate of that step, which would be rate = k[NO2][Cl2].

Although the mechanism seems to involve NO2Cl, it is not included in the rate law expression because it is an intermediate that is quickly consumed in the fast step, thereby standing in dynamic equilibrium with its reactants and having its concentration determined by them.