Stoichiometry of Methane Combustion

Steps:

• Balanced equation: CH₄ + 2O₂ → CO₂ + 2H₂O (1 mole CH₄ requires 2 moles O₂).
• Moles of CH₄: molar mass = 16 g/mol, so 40 g / 16 g/mol = 2.5 moles.
• Moles of O₂ needed: 2.5 moles CH₄ × 2 moles O₂/mole CH₄ = 5 moles O₂.
• This is the minimum (stoichiometric) amount for complete combustion.

Why D is correct:

• Matches the 1:2 mole ratio from the balanced combustion equation, providing exact oxygen molecules (O₂) for full reaction without excess.

Why the others are wrong:

• A. 1.88 moles: Underestimates ratio, possibly from erroneous 0.75:1 stoichiometry.
• B. 2.50 moles: Assumes incorrect 1:1 ratio, ignoring need for 2 O₂ per CH₄.
• C. 3.75 moles: Uses flawed 1.5:1 ratio, which does not balance the equation.

Final answer: D