2.0 g of H2 gas reacts with 32 g of O2 gas to form water. Assuming the reaction goes to completion, how many grams of water will be produced?

In order to solve this problem, the balanced chemical equation of the reaction must be used. This gives the equation:

2H2 + O2 - - > 2H2O

Next, the moles of the reactants must be used in order to apply their stoichiometric relationships. Note that 1 mole of oxygen needs 2 moles of hydrogen for the reaction proceed. Since there is only 1 mole of H2, only 0.5 moles of oxygen are consumed.

moles H2 = 2 g / 2g/mol = 1 mole H2

moles O2 = 32 g / 32g/mol = 1 mole O2

2H2 + O2 - - > 2H2O

i 1 1 0

c 1 0.5 1

e 0 0.5 1

Assuming the reaction will proceed, there will be an excess of 0.5 mol O2 and a product of 1 mol H2O. This gives 18 grams of water.