Le Chatelier's Principle for Gas Equilibrium Shift

Steps:

• Reaction Q(g) ⇌ 2R(g) has 1 mol gas reactant vs. 2 mol products; forward is endothermic (ΔH > 0).
• Equilibrium shifts right to favor more R molecules.
• Volume change affects concentration like pressure; increasing volume lowers pressure, favoring side with more moles.
• Other factors (catalyst, temperature, pressure) do not favor products.

Why D is correct:

• Increasing volume decreases pressure, shifting equilibrium right to the side with more gas moles (2R vs. Q), per Le Chatelier's principle.

Why the others are wrong:

• A: Catalyst speeds forward and reverse equally, causing no net shift.
• B: Decreasing temperature favors exothermic direction (reverse here), shifting left.
• C: Increasing pressure favors fewer gas moles (left side), shifting left.

Final answer: D