The effect of addition of helium gas to the following reaction in equilibrium state, is : $\mathrm{PCl}_{5}(\mathrm{~g}) \rightleftharpoons \mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})$

(A) the equilibrium will shift in the forward direction and more of $\mathrm{Cl}_{2}$ and $\mathrm{PCl}_{3}$ gases will be produced.; (D) addition of helium will not affect the equilibrium.

(B) the equilibrium will go backward due to suppression of dissociation of $\mathrm{PCl}_{5}$.

(C) helium will deactivate $\mathrm{PCl}_{5}$ and reaction will stop.

JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Equilibrium

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The effect of addition of helium gas to the following reaction in equilibrium state, is :

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

(A)the equilibrium will shift in the forward direction and more of $Cl_{2}$ and $PCl_{3}$ gases will be produced.✓ Correct
(B)the equilibrium will go backward due to suppression of dissociation of $PCl_{5}$ .
(C)helium will deactivate $PCl_{5}$ and reaction will stop.
(D)addition of helium will not affect the equilibrium.✓ Correct

Answer: (A), (D)

Solution

Adding an inert gas such as helium disturbs an equilibrium only if it alters the partial pressures of the reacting species. At constant volume the partial pressures of

PC l_{5}

PC l_{3}

and

C l_{2}

are unchanged, so the position of equilibrium is undisturbed. At constant total pressure the added helium expands the volume and lowers every partial pressure, and because the forward reaction increases the number of gaseous moles the system responds by dissociating more

PC l_{5}

. Thus at constant volume the equilibrium is unaffected, while at constant pressure it shifts forward to form more

PC l_{3}

and

C l_{2}

JEE Main · 2023 · 01 Feb 2023 · Shift 2 · One or more correct options

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JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Equilibrium

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