Discuss the application of LE Chatellier's principle for the industrial synthesis of Ammonia and sulphur trioxide.

Explanation

Application of Le Chatelier.s principle to
`N_2(g)+3H_2(g) hArr 2NH_3(g), DeltaH=-92 kJ`
1) Effect of pressure : Increase of external pressure on the reaction at equilibrium favours the reaction in the direction in which the volume or the number of molecules decreases In the above reaction of formation of ammonia forward reaction involves decrease in volume or number of molecules. So .high pressure is favourable for the formation of ammonia: Hence ammonia is manufactured at 200 atm pressure.
2) Effect of temperature : In a reversible reaction if the forward reaction is exothermic, the backward reaction will be endothermic. High temperature favours the endothermic reaction while low temperature favours the exothermic reaction. Since the formation of ammonia is exothermic reaction low temperature is favourable for the manufacture of ammonia. But at low temperature the reaction is slow. So an optimum temperature of about-725 - 775 K is used.
3) Effect of catalyst : To increase the rate of formation of ammonia iron powder mixed with molybdenum powder is. used as catalyst. Molybdenum acts as promoter to iron catalyst:
4) Effect of concentration : Increase in concentrations of reactants increases the rate of forward reaction. Removal of the products from reaction mixture decreases the rate of backward reaction. So more ammonia can be obtained by increasing the concentration of `N_2` and `H_2` and removing . the `NH_3` formed at regular intervals.
Optimum conditions for the synthesis of ammònia are Pressure = 200 atm
Temperature = 725-775 K
Catalyst = - Fe
Promoter = Mo