In a chemical reaction, reactants that are not used up when the reaction is finished are called excess reagents. The reagent that is completely used up or reacted is called the limiting reagent, because its quantity limits the amount of products formed. The limiting reactant or limiting reagent is the first reactant to get used up in a chemical reaction. Once the limiting reactant gets used up, the reaction has to stop and cannot continue and there is extra of the other reactants left over. Those are called the excess reactants. The reactant that produces a lesser amount of product is the limiting reagent. The reactant that produces a larger amount of product is the excess reagent. To find the amount of remaining excess reactant, subtract the mass of excess reagent consumed from the total mass of excess reagent given.
