Question

Choose the correct rate law for the elementary reversible reaction 3A ⇌ B + 2C.

(a) –rA = kCA^3 – CBCC^2/KC

(b) –rA = k[CA^3 – CBCC^2KC]

(c) –rA = k[CA^3 – CBCC^2]/KC

(d) –rA = k[CA^3 – CBCC^2/KC]

The question was posed to me in an online interview.

I would like to ask this question from Reversible Reactions Rate Laws topic in portion Rate Laws and Stoichiometry of Chemical Reaction Engineering

Answer 1

Correct choice is (d) –rA = k[CA^3 – CBCC^2/KC]

Easiest explanation: Let’s say the rate constant for the forward reaction is k1 and for the backward reaction it is k2.

Rate of disappearance of A = k1CA^3

Rate of formation of A = k2CBCC^2

-rA = k1CA^3 – k2CBCC^2. We know that KC = k1/k2. So, -rA = k[CA^3 – CBCC^2/KC].