Question

The degree of dissociation of PCl5(1) obeying the equilibrium, PCl5 $\rightleftharpoons$PCl3 + Cl2 , is approximately related to the pressure at equilibrium by (given a<<1):

• A. $\alpha \propto P$
• B. $\alpha \propto \frac{1}{\sqrt{P}}$
• C. $\alpha \propto \frac{1}{P^{2}}$
• D. $\alpha \propto \frac{1}{P^{4}}$

Answer 1

Answer: (B)

$\alpha \propto \frac{1}{\sqrt{P}}$

Answer 2

$K_{P} = \frac{\alpha^{2}}{1 - \alpha^{2}}P \approx \alpha^{2}P.$

so, $\alpha \approx \sqrt{\frac{K_{P}}{P}}$