Q.How is ammonia manufactured by Haber's process? Explain the reactions of ammonia with -

Haber's process synthesises ammonia from N2 and H2 under catalysis; ammonia also forms soluble ammine complexes with Zn²⁺, Cu²⁺ and Ag⁺ salts.

Manufacture of ammonia — Haber's process:

Ammonia is manufactured industrially from its elements by the reversible, exothermic reaction:

$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g), \qquad \Delta H = -92.4 \text{ kJ mol}^{-1}$

Optimum conditions (by Le Chatelier's principle, balancing rate and yield):

• Catalyst: finely divided iron, with molybdenum as a promoter, to speed up attainment of equilibrium.
• Temperature: about 700 K (moderately high, as a compromise between fast rate at high T and higher yield, since the forward reaction is exothermic, at lower T).
• Pressure: about 200 atm (high pressure favours the forward reaction, since it proceeds with a decrease in the number of gas moles).

Reactions of ammonia (aqueous, NH4OH) with metal salts:

1. With ZnSO4(aq): Aqueous ammonia first precipitates white zinc hydroxide: $ZnSO_4 + 2NH_4OH \rightarrow Zn(OH)_2\downarrow + (NH_4)_2SO_4$ Excess ammonia dissolves the precipitate, forming a soluble complex, tetraamminezinc(II) sulphate: $Zn(OH)_2 + 4NH_4OH \rightarrow [Zn(NH_3)_4]SO_4 + 4H_2O$
2. With CuSO4(aq): A pale blue precipitate of copper(II) hydroxide forms first: $CuSO_4 + 2NH_4OH \rightarrow Cu(OH)_2\downarrow + (NH_4)_2SO_4$ Excess ammonia dissolves it, giving a characteristic deep blue soluble complex, tetraamminecopper(II) sulphate: …