First, state the balanced equation that represents the combustion:
CH4 + 2O2 → CO2 + 2H2O
Second, state the molar ratios: 1 mol CH4 : 1 mol CO2.
Third, given that at constant temperature and pressure, the volume of an ideal gas is proportinal to the number of moles, you can state the volumetric proportion:
1 Liter of CH4 : 1 Liter of CO2.
Fourth, use the volumetric proportion:
2.0 Liter CH4 * 1 Liter CO2 /1 Liter CH4 = 2.0 Liter CO2.
Answer: 2.0 Liter CO2.
