The reaction
A+2B⟶products
is found experimentally at 400 K to obey the rate law
rate=k[B]2.
A chemist proposes the following three-step mechanism in which C is an intermediate generated and consumed during the sequence:
1. A+B→C (fast)
2. C+B→products (slow)
3. C→A (fast)
A colleague objects that the proposed mechanism cannot reproduce the observed kinetics.
(a) Derive the rate law predicted by the proposed mechanism. Express the rate solely in terms of the concentrations of A and B.
(b) Compare the derived rate law with the experimental rate law and state whether they are consistent. Provide quantitative or algebraic justification.
(c) The chemist suggests modifying the mechanism by making Step 1 the slow step and Step 2 fast. Determine whether this modification would now agree with the experimental kinetics. Show your reasoning clearly.
(d) Summarize the general criterion that any valid mechanism for this reaction must satisfy in order to be compatible with the experimentally observed rate law.