Stoichiometry deals with the quantitative relationships that exist between the reactants and products in chemical reactions. In stoichiometry, the Law of Conversation of Matter must be followed. The balanced chemical reaction equation gives the mole ratios of all reactants and products involved. The stoichiometric (equimolar) amount of reactants indicates the exact amount needed for all reactants to be used up simultaneously as the reaction proceeds to completion. If there are not stoichiometric amounts of all reactants, the reactant(s) that are used up at the completion of the reaction are the limiting reactant(s), and the remaining reactants are the reactants in excess.