1 mole of gas at STP = 22.4 L
Reaction:
2H₂(g) + O₂(g) → 2H₂O(l)
mole oxgen as a limiting reactant
mole oxygen: mass : molar mass = 55 g : 32 = 1.719
mole water H₂O based on mole oxygen as a limiting reactant
mole H₂O from reaction coefficient: 2/1 x mole O₂ = 2/1 x 1.719 = 3.438
liters H₂O at STP = 3.438 x 22.4 L = 77.0112 L