Question

Nitrogen, ${{\text{N}}_{\text{2}}}$, is the most abundant gas in the earth’s atmosphere and is very unreactive. State why ${{\text{N}}_{\text{2}}}$ is very unreactive?

Answer 1

The stability of a substance makes it unreactive. The stability of the substance depends upon many factors such as stability of bonds, activation energy, etc. Let us discuss the stability of the $N_2$ molecule.

Complete answer:
Dry air in the atmosphere contains 78 % nitrogen by volume.
So, nitrogen is most abundant but is unreactive.
The reasons for un-reactivity of nitrogen are as follows:
- Presence of triple bond.
- High activation energy.
- Nitrogen is found in nature in diatomic form. Both the nitrogen atoms are bound by a triple bond.
The decreasing order of stability of the bonds is as follows:
As the number of bonds increases, the stability of bonds increases.
Thus, Triple bond > Double bond > Single bond.
So, a Triple bond is a highly stable bond.
Thus due to the presence of a highly stable triple bond the nitrogen is unreactive.
Activation energy is the energy required to break the bond of reactant and form a transition state. As the nitrogen is very stable, it's activation energy to break the nitrogen-nitrogen triple bond is very high which makes the nitrogen unreactive.
Therefore, due to the very stable triple bond and requirement of high activation energy, the nitrogen is unreactive.

Note: The stability of bonds and high activation energy is directly proportional to the un-reactivity of a substance. The atmospheric nitrogen is highly stable but it reacts during thunderstorms due to lighting strikes. The temperature of the lighting strike is 50,000 degrees Fahrenheit.