Question

Which of the following statements are true in the case of reversible elementary reactions?

• A. Rate of forward reaction is always very large.
• B. Rate of backward reaction is very slow in the end.
• C. Rate of forward reaction is very large at the beginning.
• D. Rate of backward reaction is very slow in the beginning.

Answer 1

The correct option is D Rate of backward reaction is very slow in the beginning.

Reversible elementary reactions or opposed elementary reactions are those reactions which take place both in the forward as well as the reverse directions simultaneously.

It makes sense for the forward reaction to have a much higher rate in the beginning and the backward reaction to have a much slower rate. This is the only way the reaction can move forward. Else it would stop before it began or even occur in reverse!

So, the rate of the forward reaction is very high in the beginning and the rate of a backward reaction is very slow in the beginning. But as the reaction proceeds, the rate of forward reaction slows down and the rate of the backward reaction increases, which makes sense according to the rate law. We gradually reach a state where the rate of forward and backward reactions are equal and we reach the infamous state known as the 'equilibrium state'.