Le Chatelier's Principle
Whenever a system which is in dynamic equilibrium is disturbed, it tends to respond in such as way as to oppose the disturbance and so restore equilibrium.
Basically, if a certain factor or condition is changed, the position of equilibrium is changed, so that one reaction is favoured (forward and reverse).
So a disrupted reaction will restore itself back to equilibrium, even if this equilibrium is in a different position.
Say we take the example of the Haber process. The forward reaction is forming ammonia from hydrogen and nitrogen. The reverse reaction is ammonia turning back into hydrogen and nitrogen. The forward reaction is exothermic (enthalpy of formation), and the reverse reaction is endothermic. So a rise in temperature, will favour the endothermic reaction, as more energy is being supplied to that reaction. This results in more reactants and less products. The increase in temperature forces the equilibrium to shift to the left, meaning the production of the reactants are favoured. But if we decrease the temperature, then we favour the exothermic, forward reaction. Therefore we shift the equilibrium to the right, and this favours the production of the products.
Continuing with the same reaction, we now need to look…