Molar Mass of Methane

Methane at 16.043 g/mol is little more than half the molar mass of air, so it is strongly buoyant: a leak rises to the ceiling and collects there, which is why gas detectors in a domestic kitchen are mounted high and propane detectors are mounted low. One mole occupies 24.06 L at 25 °C and 101.325 kPa, so a standard cubic metre of methane is 41.6 mol, or 667 g.

Combustion arithmetic follows directly: CH₄ + 2 O₂ → CO₂ + 2 H₂O means 16.043 g of methane yields 44.009 g of CO₂, a mass ratio of 2.74, and releases 890 kJ as higher heating value. Pipeline natural gas is not pure methane (typically 85–95 %, with ethane, propane and inerts making up the balance) so a custody-transfer calculation uses a gas chromatograph and a weighted molar mass rather than this number alone.