Q.Discuss the principles involved in the preparation of ammonia by Haber's process. What happens when

Ammonia is manufactured by the Haber process (N2+3H2 <=> 2NH3 over an iron catalyst, high pressure, moderate temperature); catalytic oxidation of NH3 over Pt gives NO; NH3 with CuSO4 solution forms a deep-blue tetraammine copper(II) complex.

Principles of Haber's process: Ammonia is manufactured industrially from its elements:

N2(g) + 3H2(g) <=> 2NH3(g), Delta H = -92.4 kJ/mol (an exothermic, reversible reaction, with a decrease in the number of gas moles on the forward side)

By Le Chatelier's principle, since the forward reaction is exothermic and reduces the number of gas moles, high pressure and low temperature would favour maximum yield of NH3. However, at low temperature the rate of reaction becomes too slow to be industrially useful. So a compromise is used: a moderately high temperature (about 700 K / 450degC) together with a catalyst (finely divided iron, with molybdenum as a promoter to enhance catalytic efficiency) is used to achieve a reasonably fast rate, along with a high pressure (about 200 atm) to shift the equilibrium towards NH3 and improve yield.

(i) NH3 heated with O2 over platinum gauze at 500degC: this is the catalytic oxidation of ammonia (the first step of Ostwald's process for manufacturing nitric acid). Ammonia is oxidised to nitric oxide:

4NH3 + 5O2 --Pt gauze, 500degC--> 4NO + 6H2O

(The NO formed is subsequently further oxidised to NO2, which is absorbed in water to give HNO3, though that continuation is beyond what's asked here.)

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