Thursday, August 11, 2011

Application of Le–Chatelier’s Principle

One of the most important industrial reactions is the synthesis of ammonia from nitrogen and hydrogen, by Haber’s Process.
N2    +   3H2   ↔   2NH3;    DH   =   – 92 KJ/mol.
Effect of Concentration:
According to Le – Chatelier’s Principle increases in concentration of N2 or H2 (reactants) will shift the equilibrium towards right i.e. forward reaction is favourable and hence production of NH3 will be more. But if concentration of NH3 is increased, then equilibrium will shift towards left i.e. backward reaction.
Effect of Temperature:
The above reaction is exothermic in forward direction and hence endothermic in backward direction. Thus according to Le – Chatliers Principle, increase in temperature will favor endothermic reaction and hence reaction will proceed in backward direction i.e. equilibrium will shift towards left. If temperature is lowered, the reaction will proceed in forward direction, because it is exothermic and hence equilibrium will shift towards right.
Effect of Pressure:
The forward reaction i.e. formation of NH3 is accompanied with decreases in number of moles and backward reaction is accompanied with increase in number of moles.
According to Le – Chatelier’s Principle increase in pressure favour that reaction which is accompanied with decrease in number of moles and hence on increasing pressure equilibrium will shift toward right i.e. forward reaction. But if pressure is decreased, the favourable reaction is one which involves increase in number of moles. So on decreasing the pressure the reaction will favour backward reaction i.e. equilibrium will shift to left.

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