Question

What will happen with the concentration of reactants when a catalyst is added to the reaction at equilibrium?
(A) Decrease
(B) Increase
(C) Remain the same
(D) Approach zero
(E) None of the above

Answer 1

Hint: If the catalyst is added to the reaction, the rate of the reaction will change as catalyst eases the reaction without harming the reaction mechanism.
Also, only one option from the above given options can be correct.

Complete answer:
Let us study the effects of addition of catalyst in the reaction,
If the catalyst is added to the reaction, both the forward and backward reaction rates will be increased factually. At equilibrium, the concentrations of reactants and products for catalysed as well as for uncatalyzed reactions are the same.
The catalyst speeds up both forward and backward reactions to the same extent. Adding a catalyst does not affect the relative rates of the two reactions taking place in forward and backward directions. Thus, it cannot affect the position of equilibrium.
Therefore, addition of catalyst in the reaction makes no difference to the position of equilibrium.
As there is no difference in equilibrium positions when a catalyst is added to the reaction, there would be no change in the concentration of the reactants as well. Generally, adding any reagent in the reaction would never hamper the concentrations of reactant.

Therefore, option (C) Remain the same is correct.

Note:
Take a note that option (E) can never be valid in this case as all the variations are mentioned in other options. One of the answers will always be present as above.