In the following system, $\mathrm{PCl}_{5}(\mathrm{~g}) \rightleftharpoons \mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})$ at equilibrium, upon addition of xenon gas at constant $T \& p$, the concentration of

(D) $\mathrm{PCl}_{3}$ will increase

(A) $\mathrm{PCl}_{5}$ will increase

(B) $\mathrm{Cl}_{2}$ will decrease

(C) $\mathrm{PCl}_{5}, \mathrm{PCl}_{3} \& \mathrm{Cl}_{2}$ remain constant

JEE Main · 2025 · 03 Apr 2025 · Shift 1 · Equilibrium

In the following system,

PCl_{5} (g) ⇌ PCl_{3} (g) + Cl_{2} (g)

at equilibrium, upon addition of xenon gas at constant

T & p

, the concentration of

(A) $PCl_{5}$ will increase
(B) $Cl_{2}$ will decrease
(C) $PCl_{5}, PCl_{3} & Cl_{2}$ remain constant
(D) $PCl_{3}$ will increase✓ Correct

Answer: (D)

Solution

Adding an inert gas at constant temperature and pressure raises the total volume, which lowers the partial pressure of every gas present. By Le Chatelier's principle the equilibrium then shifts toward the side with the greater number of gaseous moles; here the forward reaction makes two moles from one. Dissociation of

PCl_{5}

is favoured, so its amount falls while those of

PCl_{3}

and

Cl_{2}

rise. The concentration of

PCl_{3}

increases.

JEE Main · 2025 · 03 Apr 2025 · Shift 1 · Single correct option

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