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COMPOUNDS OF NITROGEN

1.   Ammonia

Ammonia is the most important of nitrogen.

Manufacture of ammonia. Ammonia can be manufactured by Haber’s process which involves the reaction:

This is a reversible exothermic reaction. The favourable conditions for high yield of ammonia can be understood by applying Le Chatelier’s principle.

(i)                 Low temperature: Since the forward reaction is exothermic. Therefore, low temperature will favour the formation of ammonia. However, an optimum temperature of about 700 K is necessary.

(ii)                High pressure: High pressure of the order of 200 atmosphere or 200 ×105 pA is required to favour the forward reaction.

(iii)              Presence of catalyst: the use of iron catalyst containing a small amount of molybdenum or potassium oxide and aluminium oxide as promoter, increases the formation of ammonia.

Details of the process

The plant required for the manufacture of ammonia is shown in Fig. 13.9. In this method a mixture of N2 and H2 in the molar ratio 1:3 is compressed to about 200 atmosphere pressure. The compressed gases are then cooled and passed through soda lime tower to free them from moisture and carbon dioxide. Then these are fed into catalyst chamber packed with iron and molybdenum. The chamber is heated electrically to about 673 K when the two gases combine to form ammonia. The reaction being exothermic, the heat evolved maintains the desired temperature and further electrical heating is not required.