Which mechanism is plausible for the reaction A + 2B ---> C + 2D, that has an ex

Question

Which mechanism is plausible for the reaction A + 2B ---> C + 2D, that has an experimentally determined rate law of: rate = k [A][B]?

A.                (step 1) A + B ----> C + D     (slow)
                    (step 2) C + B   ----> D            (fast)

B.                (step 1) A + B ----> D + E    (slow)
                    (step 2) E + B ----> C + D     (fast)

C. (step 1) A + 2B ----> E + F      (slow)
                                (step 2) E + F   ----> B + D      (fast)
                                (step 3) D   ---->   2C (fast)

D. (step 1) B + B ----> C + E    (slow)
       (step 2) E + A ----> D            (fast)

Explanation / Answer

Answer: B

From the rate law of rate = k [A][B]

it is clear that the rate of the reaction is dependent on concentration of A and B in one fold.

It is known that slow step of the mechanism is rate determing step.

In the given options, slow step having involved one A and one B is option a and option b.

But in option a the C formed is again reacting with B to give D. that means there is no net C formed, so it ic incorrect.

then option B siuts perfect to the reaction given and rate law given.

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