What effect does temperature change have on an equilibrium reaction?

First, it depends on whether the forward reaction is exothermic or endothermic. Lets use the formation of ammonia as an example: N2 + 3H2 <-> 2NH3. The forward reaction is exothermic, so it releases energy into its surroundings. If we were to increase the temperature is a closed system, the equilibrium would shift in order to reduce the temperature. The endothermic reaction, the reverse reaction, would be favoured as it would use up this energy. Therefore the equilibrium would shift the the right. If the forward reaction were endothermic or the temperature was reduced, the opposite would happen.