Higher yield of NO in N₂ (g)+O₂ (g) ⇌ 2NO(g) can be obtained at [∆H of the reaction = +180.7 kJ mol^–1]

A.    Higher temperature

B.    Lower temperature

C.    Higher concentration of N₂

D.    Higher concentration of O₂

Choose the correct answer from the options given below :

To increase the equilibrium yield of NO in the reaction $N$₂ + O₂ ⇌ 2NO we apply Le Chatelier’s principle, which predicts how a system at equilibrium responds to changes in temperature and concentration.

1. Temperature effect
The reaction is endothermic, with ΔH = +180.7 kJ mol^–1. Adding heat therefore supplies reactants with the energy needed to form products. According to Le Chatelier, increasing temperature shifts the equilibrium toward the products, raising the amount of NO formed. Thus, higher temperature (option A) favours a higher yield.

2. Concentration of N₂
The reaction consumes N₂ as a reactant. Increasing its concentration raises the reaction quotient Q, making Q < K (the equilibrium constant). The system then proceeds forward to restore equilibrium, producing more NO. Therefore, a higher concentration of N₂ (option C) increases the yield.

3. Concentration of O₂
Similarly, O₂ is also a reactant. Raising its concentration has the same effect as for N₂: the equilibrium shifts to the right, generating additional NO. Hence, higher O₂ concentration (option D) also boosts the yield.

4. Lower temperature (option B)
Because the reaction is endothermic, lowering the temperature would shift the equilibrium toward the reactants, decreasing the NO yield. Therefore, option B does not contribute to a higher yield.

Combining the valid conditions, the correct set of factors that increase NO production is:

A, C, D only