Ammonia is manufactured by Haber's process —

(a) Under what conditions do the reactants combine to form ammonia? Give a balanced equation for the reaction.

(b) In what ratio by volume, are the above gases used?

(c) State one possible source of each reactant used in Haber Process.

(d) State whether the formation of ammonia is promoted by the use of high pressure or low pressure?

(e) Mention two possible ways by which ammonia produced is removed from unchanged gases.

(f) What is the function of

    (i) finely divided iron,

    (ii) molybdenum

in the above process?

(g) What is the percentage formation of ammonia?

(h) How can this percentage formation be increased?

(a) Nitrogen reacts with hydrogen under specific conditions liberating ammonia

N₂ + 3H₂ ⇌ 2NH₃ + Δ

Conditions :

Temperature : 450-500°C [Optimum temperature]

Pressure : 200 to 900 atmospheres [Optimum pressure]

Catalyst : Finely divided iron [Fe]

Promotor : Molybdenum [Mo]

[Catalyst - iron [III] oxide [Fe₂O₃] may also be used containing promoters about 1% K₂O and 3% Al₂O₃]

(b) According to the above equation, nitrogen and hydrogen combines in 1:3 ratio by volume.

(c) Nitrogen is obtained by fractional distillation of liquid air. Hydrogen is obtained from the water gas (Bosch process) or from natural gas.

(d) The formation of ammonia is promoted by the use of high pressure as it favours the forward direction.

(e) Two possible ways by which ammonia produced is removed from unchanged gases are:

1. By Liquefaction — ammonia is liquefied easily as compared to nitrogen and hydrogen.
2. By Absorbing in water — because ammonia is highly soluble in water, as hydrogen and nitrogen are very slightly soluble.

(f) Function of finely divided iron and molybdenum are:

1. Finely divided iron increases the rate of reaction.
2. Molybdenum acts as a promoter to increase the efficiency of the catalyst.

(g) 15%

(h) The unchanged nitrogen and hydrogen are recirculated through the plant to get more ammonia, by this way we can achieve 98% of ammonia.