Le Chatelier's principle applied to endothermic, gas-phase equilibrium

Steps:

• Identify the reaction as endothermic (ΔH > 0), so heat favors products.
• Count moles: reactants 2 mol, products 4 mol, so low pressure favors products.
• Apply Le Chatelier: high temperature shifts right for endothermic; low pressure shifts right for increased moles.
• Combine: low pressure and high temperature maximize H₂ yield.

Why C is correct:

• Low pressure and high temperature both shift equilibrium right per Le Chatelier's principle for reactions with more product moles and endothermic nature.

Why the others are wrong:

• A: High pressure shifts left (fewer moles); low temperature shifts left (exothermic reverse).
• B: High pressure shifts left despite high temperature favoring right.
• D: Low temperature shifts left despite low pressure favoring right.

Final answer: C