Chemistry: Animation, Video, and Laboratory Activity

The effect of changing the temperature of equilibrium system can be predicted from a knowledge of the heats of reaction. If the temperature of a system is lowered, the exothermic reaction is favoured. If the temperature isincreased, the endhotermic reaction is favoured.

The forward reaction therefore absorbs heat from the surroundings and the reverse reaction releases heat to the surroundings. According to Le Chatelier’s principle, if the temperature of an equilibrium system is increased the system will adjust to re-establish equilibrium in such a way as to decrease the temperature. Therefore in re-establishing equilibrium the endothermic reaction is favoured as this absorbs heat from the surroundings and would tend to decrease the temperature. In the N2O4/NO2 system this would result in an increase in the concentration of NO2 and a decrease in the cpncentration of N2O4.
If the temperature of the equilibrium system was reduced the system would re-establish equilibrium by favouring the exothermic reaction. This would tend to increase the temperature of the surroundings, partially counteracting the change. In the N2O4/NO2 system, more N2O4 and less NO2 would be present when equilibriuym was re-established.