Gas-phase dissociation equilibrium – effect of added species and pressure For the equilibrium PCl5 ⇌ PCl3 + Cl2 (all gases), identify the incorrect statement about the degree of dissociation of PCl5 under the listed changes.

Introduction / Context:
Le Châtelier’s principle predicts how an equilibrium shifts when conditions change. For the dissociation PCl5 ⇌ PCl3 + Cl2, the product side has more moles of gas than the reactant side. Pressure changes and additions of reacting or inert gases can shift the equilibrium and hence the degree of dissociation α.

Given Data / Assumptions:

• Stoichiometry: 1 mole ⇌ 2 moles (increase in gaseous moles on dissociation).
• Ideal gas behavior approximation.
• Comparisons at the same temperature.

Concept / Approach:
Adding a product (Cl2) increases its partial pressure and shifts equilibrium to the left, reducing dissociation. Increasing total pressure favors the side with fewer moles (left), again reducing dissociation. Adding an inert gas at constant pressure allows volume to increase to keep pressure fixed; this expansion favors the side with more moles (right), increasing dissociation. Thus, each specific statement (a), (b), and (c) is correct; therefore, the prompt asking for the “wrong” statement has answer “none of these.”

Step-by-Step Solution:

Verification / Alternative check:
Equilibrium constant in terms of partial pressures Kp is unchanged at fixed T; qualitative shifts follow from how partial pressures adjust to maintain Kp under constraints.

Why Other Options Are Wrong:

• Each of (a), (b), (c) correctly describes the shift; none is wrong.

Common Pitfalls:
Confusing constant-pressure vs. constant-volume addition of inert gas; at constant volume, adding inert gas does not change partial pressures and has no effect on equilibrium.

Final Answer:
none of these