- Le Chatelier’s Principle can be used to predict the effect of changes in temperature on systems in equilibrium
- To make this prediction it is necessary to know whether the reaction is exothermic or endothermic
- The following table summarises how a temperature change alters the position of equilibrium:
Effect of Temperature Changes on an Equilibrium Table
Iodine monochloride reacts reversibly with chlorine to form iodine trichloride:
2ICl (l) + Cl2 (g) ⇌ ICl3 (s)
dark brown yellow
When the equilibrium mixture is heated, it becomes dark brown in colour. Explain whether the backward reaction is exothermic or endothermic.
- The equilibirum has shifted to the left as the dark brown colour means that more of the ICl is produced. Increasing the temperature moves the equilbrium in the endothermic direction, so the reverse reaction is endothermic
Remember all reversible reactions are exothermic in one direction and endothermic in the other.