Question

The reaction of nitrogen with oxygen to form nitric oxide is:
(A) Exothermic reaction
(B) Endothermic reaction
(C) Thermal balance reaction
(D) None of these

Answer 1

Hint: Think about the stability of the reactants. If the reactants are stable, that means they have very less energy and if the reactants are unstable, they have high energy. Think whether this reaction will take place spontaneously.

Complete step by step solution:
- Nitrogen and oxygen both exist in the diatomic state in elemental form. They are highly stable gases present in the atmosphere.
- One oxygen atom forms a double bond with another oxygen atom. Whereas, one nitrogen atom forms a triple bond with another nitrogen atom. So, nitrogen has the shortest bond length and is highly stable. So, is true for oxygen, it also has small bond length and is highly stable.
- Since both the reactants, oxygen gas and nitrogen gas are stable at room temperature, they will have very low energy, very short bond lengths and high bond strengths.
- Now, for any reaction to occur, bond cleavage should happen. Here, bond strength is very high so, bond cleavage won’t happen easily.
- For bond cleavage to occur, external energy needs to be supplied in the form of heat to make the reactants unstable and break their intramolecular bonds. Therefore, this is a non-spontaneous reaction.
- Oxygen and nitrogen will not react with each other at ambient temperature and therefore, in order for the reaction to take place, the temperature of the system is increased by multiple folds.
- This reaction can only occur at extremely high temperature or naturally when lightning strikes.
- The reaction is given as,
\[{{N}_{2}}+{{O}_{2}}\xrightarrow{\Delta }2NO\]
- Therefore, since energy is absorbed by the reactants, this reaction is endothermic in nature.

Therefore, the correct answer is option (B).

Note: Remember the reaction in which energy is absorbed by the reactants to form products is an endothermic reaction and is always non-spontaneous. The reaction in which energy is released out of the system is an exothermic reaction and is always spontaneous in nature.