First, we will use the ideal gas law to determine the number of moles of the mixture that was present.
n = PV/RT
n = 1 * 5.04 / 0.082 * (273.15 + 0)
n = 0.225 moles
Let the moles of propane be P and the moles of methane be M.
P + M = 0.225
Next, we find the moles of carbon dioxide formed:
Moles = mass / Molecular weight
Moles = 19.4 / 44 = 0.441
Each mole of propane produces 3 moles of carbon dioxide and each mole of methane produces one mole of carbon dioxide. So:
3P + M = 0.441
Subtracting the first equation from the second, we get:
2P = 0.216
P = 0.108 moles
M = 0.225 - 0.108
M = 0.117
Fraction of propane = 0.108/0.225 = 0.48
Fraction of methane = 0.52