Nitrogen

Nitrogen:

Preparation:

Nitrogen, the principle gas of atmosphere (78 % by volume) is separated industrially from liquid air by fractional distillation

Pure nitrogen gas can be obtained by the thermal decomposition of sodium azide about 575 K

2NaN₃ 2→ Na + 3N₂

It can also be obtained by oxidising ammonia using bromine water

8NH₃ + 3Br₂ → 6NH₄Br + N₂

Properties

Nitrogen gas is rather inert. Terrestrial nitrogen contains 14.5% and 0.4% of nitrogen-14 and nitrogen-15 respectively. The later is used for isotopic labelling. The chemically inert character of nitrogen is largely due to high bonding energy of the molecules 225 cal mol-1 (946 kJ mol-1). Interestingly the triply bonded species is notable for its less reactivity in comparison with other iso-electronic triply bonded systems such as -C≡C-, C≡O, X-C≡N, X-N≡C, -C≡C-, and -C≡N. These groups can act as donor where as dinitrogen cannot. However, it can form complexes with metal (M→ N≡N) like CO to a less extent.

The only reaction of nitrogen at room temperature is with lithium forming Li₃N. With other elements, nitrogen combines only at elevated temperatures. Group 2 metals and Th forms ionic nitrides.

6Li + N₂ → 2Li₃N

3Ca + N₂→^{red hot} → Ca₃N₂

2B + N₂→^{bright red hot}→ 2BN

Direct reaction with hydrogen gives ammonia. This reaction is favoured by high pressures and at optimum temperature in presence of iron catalyst. This reaction is the basis of Haber’s process for the synthesis of ammonia.

With oxygen, nitrogen produces nitrous oxide at high temperatures. Even at 3473 K nitrous oxide yield is only 4.4%.

2N₂ + O₂ → 2N₂O

Uses of nitrogen

·           Nitrogen is used for the manufacture of ammonia, nitric acid and calcium cyanamide etc.

·           Liquid nitrogen is used for producing low temperature required in cryosurgery, and so in biological preservation .