LeChatelier's principle states that when a stress is imposed on a system, the equilibrium will react to counteract the stress. If a reaction is to the left, the equilibrium will shift to the left to counteract the position of equilibrium. In the Haber process the reaction between nitrogen and oxygen is exothermic.
[tex]N_2 + 3H_2 \implies 2NH_3[/tex].
So we lower the temperature. The low temperature cause the reaction to produce more heat to counteract the low temperature. When more heat is produced, the reaction shifts to the right and produces more ammonia.
