Stoichiometry help

Question

When 27.50 liters of oxygen gas reacts with excess hydrogen gas at STP how many grams of water is produced?

2 H2 + O2 —> 2 H2O

Answer 1

This is a two part question. You are given O2 in Liters, but in order to find H2O in grams you first must convert O2 to moles either using the ideal gas law PV=nRT or the relationship that 1 mole of a gas at STP will occupy 22.4.Liters and then use stoichiometry to calculate the moles of H2O and then convert to grams. Lets use the relationship that 1 mole of a gas will occupy 22.4.L at STP as it is the simplest mathematically but both approaches will give the same answer.

27.5 L O2 X 1mole O2/22.4 L = 1.227 moles O2

2H2 + O2 = 2H2O

Now using the molar ratio of 2 moles H2O/1 mole O2

1.227 mol O2 X 2mol H2O/1 mol O2 = 2.454 mol H2O

Converting moles of H2O to grams

2.454 mol H2O X 18 grams of H2O/1 mol H2O = 44.172 grams H2O