Question

Identify the reaction for which, at equilibrium, a change in the volume of the closed reaction vessel at a constant temperature will not affect the extent of the reaction

• A. CaCO₃ (𝑠) ⇌ CaO(𝑠) + CO₂(𝑔)
• B. H₂ (𝑔) + I₂ (𝑔) ⇌ 2HI(𝑔)
• C. 2NO₂ (𝑔) ⇌ N2O₄ (𝑔)
• D. CO₂ (𝑠) ⇌ CO₂ (𝑔)

Answer 1

The Correct Option is B

At equilibrium, the effect of a change in volume is determined by the number of gaseous moles on either side of the reaction.

• If the total number of gaseous moles changes during the reaction, a change in volume will shift the equilibrium to favor the side with more or fewer moles of gas (as per Le Chatelier’s principle).
• If the total number of gaseous moles remains the same, a change in volume will not affect the extent of the reaction.

Let’s analyze each option:

• (A) CaCO₃(s) ⇌ CaO(s) + CO₂(g) : This reaction involves a change in the number of moles of gas (0 → 1). Hence, a change in volume will affect the equilibrium.
• (B) H₂(g) + I₂(g) ⇌ 2HI(g) : The number of gaseous moles on both sides of the reaction is the same (2 → 2). Thus, a change in volume will not affect the equilibrium.
• (C) 2NO₂(g) ⇌ N₂O₄(g) : This reaction involves a change in the number of gaseous moles (2 → 1). Hence, a change in volume will affect the equilibrium.
• (D) CO₂(s) ⇌ CO₂(g) : This reaction involves a change from a solid to a gas (0 → 1). Hence, a change in volume will affect the equilibrium.