The stoichiometric ratio refers to the proportional relationship between the quantities of reactants and products in a chemical reaction. It is derived from the balanced chemical equation, which shows how many molecules of each substance are involved. For example, in the reaction of hydrogen and oxygen to form water, the stoichiometric ratio is 2:1:2, meaning two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. Understanding stoichiometric ratios is essential for predicting how much product can be formed from given amounts of reactants. This concept is widely used in fields like chemistry, pharmacy, and engineering to ensure reactions are efficient and to minimize waste.