Question

For the chemical reaction:

A + B  3 C

observed to have a rate law of Rate = k [B]², the following reaction mechanism has been proposed.

2 B  D (slow)

D + A  3 C + B

In your evaluation of the reaction mechanism you would conclude the mechanism is:

A) a plausible representation of the reaction

B) an implausible representation as the predicted rate law does not match the observed rate law

C) an implausible representation as the mechanism does not result in the reaction given

D) an implausible representation as the mechanism has more than three reactants in a elementary step

E) an implausible representation as the mechanism has more than three products in a elementary step

Please explain your answer

Answer 1

We know that the slow step of a reaction is the rate determining step of the reaction. Also the rate=k[B]²

This shows that there are 2 B (reactant) in the slow rate determining step which is the slow step of the proposed mechanism

Also in the next step, the intermediate D formed in the slow step reacts with A to give 3 C and B

Now if we add up the two steps we get the desired reaction. So the given mechanism is the plausible representation of the reaction (option A)