19. Dinitrogen: Preparation: heat NH4 Cl( aq) + NaNO2( aq) → N2( g) + 2H2 O( l) + NaCl( aq)
heat( NH4) 2 Cr2 O7 →
N2
+ 4H2 O + Cr2
O3
() heat
Ba N3 2
→ Ba + 3 N2
Properties:
It is a colouless, odourless, tasteless and non – toxic gas. It is chemically un-reactive at ordinary temperature due to triple bond in
N ≡ N which has high bond dissociation energy.
20. Ammonia: Ammonia molecule is trigonal pyramidal with nitrogen atom at the apex. It has 3 bond pairs and 1 lone pair. N is sp 3
hybridised.
Preparation: Haber’ s process:
N2( g) + 3H2( g) YZZZZZZX2 NH3( g) Pressure = 200 x10 5 Pa fH o = − 46.1 kJ mol −1
Temperature = 773 K Catalyst is FeO with small amounts of K2O and Al2O3