Gas Stoichiometry

Gas laws can be combined with basic stoichiometry to solve for amounts of gaseous reactants and products. Since we usually measure gas parameters like pressure, and volume rather than mass or number of molecules it useful to have some practice with this type of calculation. Here is a sample problem.

A laboratory scale method for reducing metal oxide is to heat it with H2. The prue metal and water are the products. What voluem of H2 at 765 Torr and 185oC is needed to form 35.5 g Cu from copper(II) oxide? SOLUTION: CuO(s) + H2(g) Cu(s) + H2O(l) The number of hydrogen moles is: 35.5g Cu x 1 mol Cu / 63.55 g Cu x 1 mol H2 / 1 mol Cu = 0.559 mol H2 V = nRT / P = (0.559 mol x 0.0821 x 458 K) / 1.01 atm = 20.8 L