Question

State and explain Le Chatelier’s principle suitably with reference to change in temperature.

Answer 1

Le Chatelier’s principle:

When a system at equilibrium is subjected to a change in any of the factors determining the equilibrium conditions of a system, system will respond in such a way as to minimize the effect of change.

Change in temperature:

1. Consider the equilibrium reaction,
   \[\ce{PCl_{5(g)} ⇌ PCl_{3(g)} + Cl_{2(g)} + 92.5 kJ}\]
2. The forward reaction is exothermic. According to Le Chatelier's principle an increase in temperature shifts the position of equilibrium to the left.
3. The reverse reaction is endothermic. An endothermic reaction consumes heat. Therefore, the equilibrium must shift in the reverse direction to use up the added heat (heat energy converted to chemical energy).
4. Thus, an increase in temperature favours the formation of PCl₃ and Cl₂, shifting the equilibrium to the right, as the reverse reaction is endothermic and consumes heat. Conversely, a decrease in temperature favours the formation of PCl₅, shifting the equilibrium to the left, as the forward reaction is exothermic and releases heat."