Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, so the mass of reactants and products are equal. To solve stoichiometry problems, the amounts of reactants and products are converted to moles using molar masses. The limiting reagent is the first reactant to be completely used up and determines how much product can be formed. Any excess reactant remains after the reaction completes.