Q.Write the process, chemical equation of the industrial manufacture of ammonia giving labelled diagram. Also write chemical equation for the reaction of ammonia with

Ammonia is made industrially by Haber's process — direct combination of $N_2$ and $H_2$ over an iron catalyst at high pressure and moderate temperature; the ammonia then forms ammine complexes with $CuSO_4$ (deep-blue tetraamminecopper(II)) and dissolves $AgCl$ (as diamminesilver(I) chloride).

(a) Haber's process — industrial manufacture of ammonia.

Reaction:

$N_2(g) + 3H_2(g) \underset{}{\overset{Fe}{\rightleftharpoons}} 2NH_3(g), \qquad \Delta H = -92\ \text{kJ mol}^{-1}$

Optimum conditions (chosen from Le Chatelier's principle — the reaction is exothermic and reduces the number of gas moles):

• Pressure: high, $\sim200\ \text{atm}$ (favours the forward, mole-reducing reaction).
• Temperature: a moderate $\sim450-500^{\circ}C$ (a compromise — low temperature favours yield but is too slow).
• Catalyst: finely divided iron with molybdenum (or $K_2O + Al_2O_3$) as promoter to speed up equilibrium.

Process (see figure): purified $N_2$ and $H_2$ in a $1:3$ ratio are compressed and passed into the catalyst chamber; the hot exit gases are cooled so that ammonia liquefies and is separated, and the unreacted $N_2 + H_2$ are recycled.

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