Question

A catalyst added to a reaction mixture
A. Increases the equilibrium constant
B. Decreases the equilibrium constant
C. Does not change the equilibrium constant
D. None of these

Answer 1

Hint: Catalyst (Greek: kata i.e., totally and lein i.e., to unfasten) is a substance that changes the rate of reaction but is recovered chemically unchanged at the end of the reaction. This process is called catalysis.

Complete Step by Step Answer:
A catalyst modifies the rate of reaction but is regained chemically unaffected at the end of the reaction.
For example, the manufacture of ammonia by Haber's process uses finely divided iron as a catalyst.
A reaction takes place due to the collision of the reactant molecules.
The minimum quantity of energy that the colliding molecules must possess to bring about a reaction is called threshold energy.
The minimum extra quantity of energy absorbed by the reactant molecules so that their energy becomes equal to a threshold value is called activation energy.
The rate of a reaction upsurge after putting in the catalyst to a reaction and in turn does not get destroyed during the reaction.
It reduces the activation energy of the reactants by enabling the decline of the energy barrier and thus conversion of reactants into products is much more effortless.
In a reversible reaction, the magnitude of decrease in the activation energy of the forward and backward reactions is the same due to the catalyst.
So, there is no overall change in the equilibrium state of a reaction.
As the catalyst does not affect the equilibrium state and hence, does not have any consequence on the equilibrium constant of the reaction as well.

So, option B is correct.

Note: Catalysts don't have any significant consequence on the rates of backward or forward reactions. So, it doesn't influence the equilibrium state and hence, does not control the equilibrium constant of the reaction.