Question

Which of the following statements is/are correct with respect to the equilibrium for equation $PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$?

• A. Decrease in pressure will increase the dissociation of $PC{l}_5$.
• B. The degree of dissociation of $PC{l}_5$ varies inversely as the square root of the pressure of the system, when it is small compared to unity.
• C. Decrease in volume of the system will increase the dissociation of $PC{l}_5$.
• D. The value of $K_P=0.041$ atm at one atmospheric pressure when the degree of dissociation is 0.2.

Answer 1

Answer: (A), (B), (D)

The correct options are
A Decrease in pressure will increase the dissociation of $PC{l}_5$.
B The degree of dissociation of $PC{l}_5$ varies inversely as the square root of the pressure of the system, when it is small compared to unity.
D The value of $K_P=0.041$ atm at one atmospheric pressure when the degree of dissociation is 0.2.

The number of moles of reactants is smaller than the number of moles of products. Hence, as the pressure will decrease, the dissociation of $PC{l}_5$ will increase.

The degree of dissociation of a gas is inversely proportional to the product P and density D of the gas.

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

With a decrease in the volume, the pressure increases. It will decrease the dissociation of $PC{l}_5.$

At 1 atm pressure, the partial pressures of $PC{l}_5,PC{l}_3$ and $C{l}_2$ are 0.667 atm, 0.167 atm and 0.167 atm respectively.

The equilibrium constant is $K_p=\frac{0.167\times 0.167}{0.667}=\mathrm{0.041.}$