In the combustion of hydrogen gas, hydrogen reacts with oxygen from the air to form water vapor. Hydrogen + Oxygen #-># water. If you burn 58.1 g of hydrogen and produce 519 g of water how much oxygen reacted?
The stoichiometrically balanced equation tells us unequivocally that
The water is stoichiometric with respect to the amount of dihydrogen. (What do I mean by this?) There was thus a stoichiometric quantity of dioxygen gas, i.e.