5. Which step of the proposed mechanism must be slow in order to agree with this rate law?

Question

he rate of formation of carbon tetrachloride from chloroform,

CHCl₃(g) + Cl₂(g) => CCl₄(g) + HCl(g)

is first order in CHCl₃ and half order in Cl₂.

Which step of the proposed mechanism must be slow in order to agree with this rate law?

1. Cl₂(g) => 2 Cl(g)

2. Cl(g) + CHCl₃(g) => HCl(g) + CCl₃(g)

3. CCl₃(g) + Cl(g) => CCl₄(g)

Detailed explanation please

the answer is: 2

Answer 1

The rate law for each step would be as follows:

(1) rate = k[Cl₂] This can't be correct because it doesn't contain a term for CHCl₃

(2) rate = k[Cl]^1/2[CHCl₃] This agrees with the experimentally determined rate law

(3) rate = k[CCl₃][Cl]^1/2 This can't be correct because it contains CCl₃ which isn't a reactant in the original equation, and also it doesn't contain CHCl₃

So, the correct answer would be (2)