The balanced equation for the reaction is as follows 2H₂ + O₂ --> 2H₂O stoichiometry of H₂ to O₂ is 2:1 number of H₂ moles - 30.0 g / 2 g/mol = 15 mol number of O₂ moles - 80.0 g / 32 g/mol = 2.5 mol limiting reactant is the reagent in which only a fraction is used up in the reaction if H₂ is the limiting reactant if 2 mol of H₂ requires 1 mol of O₂ then 15 mol of H₂ requires 1/2 x 15.0 = 7.5 mol of O₂ but only 2.5 mol of O₂ is required this means that O₂ is the limiting reagentt and H₂ is in excess
