1. If 5.2 L of hydrogen and 2.6 L of oxygen at STP react to yield water, how many moles of water are formed?

2H₂ + O₂ → 2H₂O
Mole ratio in reaction H₂ : O₂ = 2 : 1

1 mole of gas occupies a volume of 22.4 L at STP.
Initial number of moles of H₂ = (5.2 L) / (22.4 L/mol) = 0.232 mol
Initial number of moles of O₂ = (2.6 L) / (22.4 L/mol) = 0.116 mol
Initial mole ratio H₂ : O₂ = (0.232 mol) : (0.116 mol) = 2 : 1
Hence, both H₂ and O₂ completely reacts.

According to the above equation, mole ratio H₂ : H₂O = 2 : 2 = 1 : 1
Number of moles of H₂ reacted = 0.232 mol
Number of moles of H₂O formed = 0.232 mol