Question

There is an error in the rate-determining step of the following proposed mechanism. Slow step: CH3(g) + Cl2(g) mc026-1.jpg CH3(g) + HCl(g) and the rate rule is k1 = [CH4][Cl2] Fast step: CH3(g) + Cl2(g) mc026-2.jpg CH3Cl(g) + Cl–(g) and the rate rule is k2 = [CH4][Cl2] Overall : CH4(g) + 2Cl2(g) mc026-3.jpg CH3Cl(g) + HCl(g) + Cl–(g) Which shows the correct rate-determining step for the mechanism?

Answer 1

The rate rule does not match B,C,D so A must be the right answer.

Answer 2

The steps with correct mechanism are given below:

1) CH₄(g) + Cl(g) → CH₃(g) + HCl(g) : This is a slow step.
The rate is given as: R1 = k₁[CH₄][Cl]

2) CH₃(g) + Cl₂(g) → CH₃Cl(g) + Cl(g): This is a fast step.
The rate is given as: Rate = k₂[CH₃][Cl₂]

∴ CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g)

Here, the slowest step will be the rate-determining step.