Question

When a catalyst is added to a system, the:
A. Value of equilibrium constant is decreased
B. The rate of forward reaction is increased and of backward reaction is decreased
C. Equilibrium concentrations are unchanged
D. Equilibrium concentrations are increased

Answer 1

Hint: A substance that functions in altering a reaction's rate is termed a catalyst. It gives an alternate pathway by which a reaction proceeds. The activation energy of the new path is less than the original.

Complete Step by Step Answer:
Let's understand what happens with the addition of a catalyst to a system. The role of the catalyst is to speed up both the forward and the backward reactions. Thus, it helps to achieve the equilibrium state early. But the concentration at equilibrium is not changed, that is, the equilibrium constant is not changed.

Let's discuss the options one by one.
Option A says the decrease of the value of the equilibrium constant on adding a catalyst to a system. Therefore, A is wrong.
Option B says that the increase of forward reaction but a decrease of backward reaction on the addition of a catalyst. Therefore, it is wrong as both backward and forward reactions increase.
Option D says that increase of equilibrium constant value on the addition of a catalyst. Thus, it is not correct.
Option C says that no change is observed in the equilibrium concentration when a catalyst is added.
Therefore, option C is right.

Note: Catalysts are classified as positive and negative catalysts. Positive catalysts function in speeding up of reaction. For example manganese dioxide, vanadium dioxide, etc. The negative catalysts lower the speed of a reaction, such as platinum.