How many grams of methane should be burned in an excess of oxygen at stp to obtain 5.6 l of carbon dioxide?

The balanced reaction that describes the reaction between methane and oxygen to produce carbon dioxide and water is expressed Ch4 +2O2 = CO2 +2H2O. We use PV=nRT to determine the moles of carbon dioxide equivalent to 5.6 L of it. For every mole of ideal gas, there is an equivalent volume of 22.4 L. Hence there are 0.25 moles of CO2. The mass of methane used is 4 grams methane.

The answer to this problem is. 67