Question

The equilibrium $N_2\left(g\right)+O_2\left(g\right)\rightleftharpoons 2NO\left(g\right)$ is established in a reaction vessel of $2.5\text{L}$ capacity. The amounts of $N_2\text{and}{O}_2$ taken at the start were $4\text{and}6\text{moles}$, respectively, and half a mole of nitrogen was used up at equilibrium. What is the molar concentration of nitric oxide at equilibrium?

• A. $0.2$
• B. $0.4$
• C. $0.6$
• D. $0.1$

Answer 1

The correct option is B $0.4$

Consider the equilibrium, $N_2\left(g\right)+O_2\left(g\right)\rightleftharpoons 2NO\left(g\right)$

	$N_2\left(g\right)$	$O_2\left(g\right)$	$NO\left(g\right)$
No. of moles initially	4 mol	6 mol	0 mol
No. of moles at equilibrium	4 - 0.5 = 3.5 moles	6 - 0.5 = 5.5 moles	$2\times 0.5=1$ mol

Molar concentration of nitric oxide (c) = Number of moles / Volume of the gas
$=\frac{1}{2.5}$
$=0.4$
(Volume of the container is taken as the volume of the gas)

Hence, option (b) is the correct answer.