Manufacturing of ammonia by Haber’s process
Ammonia is a colourless pungent smelling gas used mostly in production of fertilizers. It is widely manufactured by Haber process from nitrogen (N2) and hydrogen (H2). The Haber process takes nitrogen gas from air and combines it with molecular hydrogen gas to form ammonia gas. Nitrogen and hydrogen are taken in the ratio of 1:3 by volume. This is an exothermic reaction, it releases energy so that the sum of the enthalpies of N2 and H2 (the reactants) is greater than the enthalpy of NH3 (the products).
N2 (g) + 3H2 (g) → 2NH3 (g) ΔH = — 92 KJmol-1
(this is a reversible reaction)
The reaction is effected by temperature, pressure and catalyst on the composition of the equilibrium mixture, the rate of the reaction and the economics of the process. The catalyst is actually slightly more complicated than pure iron. It has potassium hydroxide added to it as a promoter — a substance that increases its efficiency.
The process can be diagrammatically shown as —
The pressure varies from one manufacturing plant to another, but is always high. At each pass of the gases through the reactor, only about 15 per cent of the nitrogen and hydrogen converts to ammonia. By continual recycling of the unreacted nitrogen and hydrogen, the overall conversion is about 98 per cent.
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