Mass of methane required to produce 22 g of CO₂ after complete combustion is _______ g.
(Given Molar mass in g mol-1 C=12.0, H=1.0, O=16.0)

Solution

Chemistry ma’am · 4 steps

Every carbon in CO₂ came from one methane, so moles of CH₄ equal moles of CO₂.

1. Balanced equation. Write the complete combustion of methane first. The coefficients give the mole ratio.

   CH₄ + 2O₂ → CO₂ + 2H₂O

2. Moles of CO2. Molar mass of CO₂ is 12 + 2 × 16 = 44 g mol⁻¹. So 22 g is 22/44 = 0.5 mol.
3. Moles to mass. The ratio CH₄ : CO₂ is 1 : 1, so 0.5 mol of CH₄ is needed. Molar mass of CH₄ is 12 + 4 × 1 = 16 g mol⁻¹, so the mass is 0.5 × 16 = 8 g.
4. So. The mass of methane required is 8 g.

The idea to keep. In stoichiometry, always go grams to moles, use the balanced equation's mole ratio, then go back to grams. Never compare masses directly.

Answer from the NTA final answer key. Solution by PrepWiser.