1) First, let's rewrite the equation:
C3H8 + 5 O2 ——> 3 CO2+ 4 H2O
When we consider the pressure is equal to 1 atm and the temperature is 273 K (0°C), we have that the volume occupied by 1 mole of any gas will always be 22.4 L. So:
22.4 L ------ 1 mol of Propane (C3H8)
2.6 L ------- x mol of Propane (C3H8)
22.4x = 2.6
x = 0.116 mol of propane
2) Now you use the equation proportion to find out the quantity of moles of water produced:
1 mol of C3H8 ----- 4 mol of H2O
0.116 mol of C3H8 ----- x mol of H2O
x = 0.46 mol of H2O
3) Now let's use the molar mass of water to find out the value in grams:
Molar mass of H2O = (2x1) + 16 = 18 g/mol
Use the following equation: mass = molar mass × mole
mass = 18 × 0.46
mass = 8.4 grams
Answer: 8.4 grams of water