Question

If the degree of dissociation of $PC{l}_5$ in the reaction $PC{l}_5\left(g\right)\iff PC{l}_3\left(g\right)+C{l}_2\left(g\right)$ at equilibrium is 0.2 and if the initial number of moles of $PC{l}_5$ is one,the total number of moles present in the gaseous mixture at equilibrium is :

• A. 2.8
• B. 1.2
• C. 1.4
• D. 1.6

Answer 1

The correct option is B 1.2

The equilibrium for the dissociation of $PC{l}_5$ is $PC{l}_5\left(g\right)\iff PC{l}_3\left(g\right)+C{l}_2\left(g\right)$.
Following table list the number of moles of various species.

	$PC{l}_5$	$PC{l}_3$	$C{l}_2$
Initial	1	0	0
Change	-0.2	0.2	0.2
Equilibrium	1-0.2	0.2	0.2

Hence, total number of moles $=1-0.2+0.2+0.2=1.2$.