Question

$4.5g$ of $PC{l}_5$ were completely vaporized at $250$ and the vapour occupied $1.7litre$ at 1 atmospheric pressure. Calculate the degree of dissociation(%), for the reaction : $PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$. Write answer as nearest integer after diving degree of dissociation calculated by 10.

Answer 1

The molar mass of phosphorous pentachloride is 208.24 g/mol

Initial vapour density D $=\frac{M.Wt}{2}=\frac{208.24}{2}=104.12$

At equilibrium, the density of the gaseous mixture $\rho =\frac{4.5g}{1.7L}=2.65g/L$

The vapour density of the equilibrium mixture $d=\frac{\rho RT}{2P}=\frac{2.65\times 0.08206\times 523}{2\times 1}=56.8$

The degree of dissociation $\alpha =\frac{D-d}{(n-1)d}=\frac{104.12-56.8}{(2-1)\times 56.8}=0.835$

Hence, the degree of dissociation is 0.835 or 83.5 %.

Answer is 8.