When 3.5 L of propane gas is completely combusted to form water vapor and carbon dioxide at 350°C and 0.950 atm, what mass of water vapor results?

The chemical reaction would be as follows:

C3H8 + 5O2 = 3CO2 + 4H2O

We are given the volume of propane gas at certain temperature and pressure. We need to assume that the gases are ideal. From this we can easily, relate things as follows:

PV = nRT

n = PV/RT = 0.950 (3.5) / 0.08205 (623.15) = 0.0650 mol C3H8

0.0650 mol C3H8 (4 mol / 1 mol C3H8) (18.02 g / mol) = 0.26 g H2O produced