Group 15 Elements
Dinitrogen ($N_2$): Preparation, Reactivity & Uses
Dinitrogen constitutes 78% of Earth's atmosphere. Due to the exceptionally strong triple bond ($N \equiv N$), it is highly inert at room temperature but reactive at higher temperatures.
1. Preparation of Dinitrogen
Nitrogen is produced commercially by liquefaction of air and in the laboratory by treating ammonium salts.
Lab Method
$NH_4Cl + NaNO_2 \rightarrow N_2 + 2H_2O + NaCl$
Thermal Decomposition
$(NH_4)_2Cr_2O_7 \xrightarrow{\Delta} N_2 + 4H_2O + Cr_2O_3$
Ultra-Pure Nitrogen
Very pure nitrogen can be obtained by the thermal decomposition of sodium or barium azide:
$2NaN_3 \xrightarrow{\Delta} 2Na + 3N_2$
Figure: Comprehensive Reaction Chart of Dinitrogen ($N_2$)
2. Chemical Properties & Reactivity
The high bond enthalpy ($941.4 \text{ kJ mol}^{-1}$) of the $N \equiv N$ bond makes dinitrogen inert at room temp. Reactivity increases significantly with temperature.
High-Temp Reactions
- With Metals: Forms ionic nitrides with active metals (Li, Mg, Ca).
Example: $6Li + N_2 \xrightarrow{\Delta} 2Li_3N$ - Haber Process: Combines with $H_2$ to form Ammonia.
$N_2 + 3H_2 \rightleftharpoons 2NH_3$ ($\Delta H = -46.1 \text{ kJ mol}^{-1}$) - With Oxygen: Forms Nitric Oxide only at very high temp ($> 2000 \text{ K}$).
$N_2 + O_2 \rightleftharpoons 2NO$
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