Question

In the reversible reaction a catalyst is the substance which
A. Increases the rate of the forward reaction
B. Decreases the value of enthalpy change in the reaction
C. Reduces the time required for reaching the equilibrium state in the reaction
D. Decreases the rate of the reverse reaction

Answer 1

Hint: Catalyst is a substance that raises the rate of a chemical reaction by not encountering any permanent chemical change. A reversible reaction is a reaction in which the transformation of reactants to products and the transformation of products to reactants happen simultaneously.

Complete Step by Step Answer:
A catalyst is a substance that cuts short the time needed for the reaction to achieve equilibrium.
Out of the given options, we have to find out which is correct about the activity of the catalyst in a reversible reaction.

A catalyst increases both the forward and reverse reaction thus helping to reach the equilibrium state more quickly. It doesn't only raise the rate of the forward reaction. So, A is incorrect.

Catalyst does not alter the value of enthalpy change in a reaction. So, B is incorrect.

Catalyst pursues an alternative direction for the reaction which needs lower activation energy.
Therefore, it increases the rate of forward and reverse reactions in equal amounts.

We know that at the equilibrium state of a chemical reaction, the rate of forward reaction is equivalent to the rate of the reverse reaction. So, the rate of forwarding and reverse reaction becomes equal much earlier when the catalyst is involved. The catalyst reduces the time needed for attaining the equilibrium state in the reaction. So, C is correct.

The catalyst increases the rate of the reverse reaction. So, D is incorrect.

So, a catalyst reduces the time needed for attaining the equilibrium state in the reaction.
So, option C is correct.

Note: A reversible reaction at equilibrium can become unstable if there is change involved in it. Examples are enhancing or reducing chemical concentrations, or temperature. If a change like this is applied, the reversible reaction will encounter a shift to undo the effect of the change in its equilibrium. This is defined as Le Chatelier’s Principle.