Chemical and Ionic Equilibrium 1 Question 17

18. Consider the following equilibrium in a closed container

$$ \mathrm{N}{2} \mathrm{O}{4}(g) \rightleftharpoons 2 \mathrm{NO}_{2}(g) $$

At a fixed temperature, the volume of the reaction container is halved. For this change, which of the following statements hold true regarding the equilibrium constant (Kp) and degree of dissociation (α) ?

(2002,3M)

(a) Neither Kp nor α changes

(b) Both Kp and α change

(c) Kp changes but α does not change

(d) Kp does not change but α changes

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Solution:

$$ \begin{aligned} & \mathrm{N}{2} \mathrm{O}{4}(g) \rightleftharpoons \underset{2}{2} \rightleftharpoons \underset{2}{2} \mathrm{NO}{2}(g) \quad  Total  1+α \ p{i}: \quad \frac{1-\alpha}{1+\alpha} p & \frac{2 \alpha}{1+\alpha} p \quad K_{p}=\frac{4 \alpha^{2}}{1-\alpha^{2}} p \end{aligned} $$

At constant temperature, halving the volume will change both p and α but Kp remains constant.