How is a limiting reactant problem different from other stoichiometry problems?
For a limiting reactant problem, you’ll have leftover of one material so you need to put all chemical species in terms of the limiting reactant. Example. for the reaction O2 + 2H2 –> 2H2O I have 2 moles of Oxygen and 2 moles of hydrogen, but I need 4 moles of Hydrogen in order to react completely with the oxygen (1:2). Therefore hydrogen is the limiting reactant in this reaction because it limits how much of O2 can react. When you’re trying to figure out how many moles of water you can generate, you’ll have to use the water’s ratio to the limiting reactant….. 2 mol hydrogen (1 mol H2O/2 mol H2) = 1 mol H2O generated. If, instead you had used Oxygen’s ratio to water, you would have got 2 mol O2 (2 mol H2O/ 2 mol O2) = 2 mol H2O See, you have to use ratio’s with the limiting reactant to figure out the moles of everything else in the reaction.