Two moles of $PCl X_{5} (g)$ dissociate in a vessel held at constant temperature, and at equilibrium the total pressure is $3.0 atm$ and the vapour density of the mixture is $69.5$ (calculated value for undissociated $PCl X_{5}$ is $104.25$ ). Select the correct statements.

Answer: A, C, D

α = (104.25 - 69.5) /69.5 = 0.50

(A true). Total moles

= 2 (1 + α) = 3.0

, not 2.5 (B false). Moles:

PCl X_{5}

1.0,

PCl X_{3}

1.0,

Cl X_{2}

1.0, so

x (Cl X_{2}) = 1/3

(C true).

K_{p} = α^{2} P / (1 - α^{2}) = 0.25 \times 3.0/0.75 = 1.0

atm (D true).