Question

The equilibrium constant in reversible reaction at a given temperature:
(A) Depends on the initial concentration of the reactants
(B) Depends on the concentration of products in equilibrium
(C) Does not depend on the initial concentrations
(D) It is not characteristic of the reaction.

Answer 1

Hint: Equilibrium constant is defined as the number which tells the relationship between the amount of products (concentration of product) and amount of reactants (concentration of product) at a given temperature during a reversible reaction (a reaction that can be reversed) when equilibrium reach.

Complete Step by Step Solution:
According to Le Chatelier's Principle, the equilibrium constant for any reversible reaction at a given temperature is always a fixed number. If you increase the concentration of reactant or product, the direction of equilibrium will change to revert the change but there will be no effect on the equilibrium constant value.

Let us assume a reversible reaction at a given temperature
\[A\text{ }+\text{ }B\rightleftharpoons 2C\text{ }+\text{ }D\]
Its equilibrium constant say Kc is defined as
\[Kc\text{ }=\text{ }\left[ C \right]{}^\text{2}\left[ D \right]/\left[ A \right]\left[ B \right]\]

Now, if we decrease the concentration of C, then the equilibrium constant value should decrease but the equilibrium shifts in forward direction to revert the change, and the concentration of product starts to decrease to increase the concentration of product as before. And the decrease in the concentration of reactant continues until the equilibrium constant attains the same value before changing the concentration of C.

Thus, only the direction of equilibrium changes to undo the change and we will get the same value of the equilibrium constant as before the change was made. So, the equilibrium constant does not depend on the initial concentration of product and reactant.
Thus, the correct option is C.

Note: It is important to note that K_p, the equilibrium constant of pressure also remains unchanged if we change the pressure of the whole reaction. On adding any catalyst the equilibrium remains the same. So what can change the equilibrium constant? It is the temperature that can affect the equilibrium constant. If we change the temperature of the system, the equilibrium constant value also changes. When forward reaction is exothermic then on increasing temperature value of equilibrium constant decreases otherwise (if forward reaction is endothermic) increases.