Question

For the equilibrium, ${{\text{H}}_{\text{2}}}{\text{ + }}{{\text{I}}_2}{\text{ }} \rightleftharpoons {\text{ 2 HI}}$ , which of the following will affect the equilibrium constant?
A ) pressure change
B ) concentration change
C ) catalyst
D ) Temperature change

Answer 1

Apply Le-Chatelier’s principle to different conditions. According to Le-Chatelier’s principle, when a system at equilibrium is subjected to a change, the equilibrium will shift in the direction, so as to minimise the effect of change.
You can change the temperature, pressure, concentration etc. In exothermic reactions, write the heat on the product side and in the endothermic reaction, write the heat on the reactant side. When you increase the temperature, you add heat to the system. When you decrease the temperature, you remove the heat from the system.

Complete answer:
The value of the equilibrium constant is independent of the change in pressure, change in the concentration of reactants or products and presence or absence of catalyst. In other words, if you change the pressure of reaction mixture, you will obtain the same value of the equilibrium. Similarly, if you change the concentration (of either reactant or product), still you will get the value of the equilibrium. Similarly, if you add a catalyst, you will only accelerate the rate of the forward and reverse reactions. However you cannot affect the value of the equilibrium constant.
The value of equilibrium constant changes with change in the temperature.
If the forward reaction is exothermic, and if you increase the temperature, you will decrease the value of the equilibrium constant. If the forward reaction is endothermic, and if you increase the temperature, you will increase the value of the equilibrium constant.

Hence, the correct option is option D ) Temperature change.

Note: Change in pressure, or concentration will affect the position of the equilibrium system. But it will not affect the value of the equilibrium constant. When a catalyst is added, it will speed up the reaction so that equilibrium is quickly attained. But the value of the equilibrium constant is not changed. A catalyst only provides an alternate pathway of lower activation energy.