Question

4 mol of ${PCl}_5$ are heated at the constant temperature in the closed container. If the degree of dissociation for ${PCl}_5$ is 0.5, then calculate the total number of moles at equilibrium.

• A. 4.5
• B. 6
• C. 3
• D. 4

Answer 1

Answer: (B)

6

$PC{l}_5\leftrightharpoons PC{l}_3+C{l}_2$

Initial C 0 0

At equil. C $(1-\alpha )$ $C\alpha$ $C\alpha$

Total number of moles at equilibrium = C $(1-\alpha )+C\alpha +C\alpha$ = C $(1+\alpha )$

Here, $\alpha$ = 0.5

Therefore, the total number of moles at equilibrium = $4(1+0.5)=6mol$