How does stoichiometry describe the quantities of substances in a chemical reaction?

Stoichiometry is the branch of chemistry that determines the proportions in which elements or compounds react with one another. It relies on the law of conservation of mass, which dictates that matter is neither created nor destroyed during a chemical reaction.12

Balancing Equations and Stoichiometric Factors

To describe these quantities, chemists use balanced chemical equations where the number of atoms of each element is identical on both sides. The coefficients used to balance these equations are known as stoichiometric factors; for example, in the reaction of methane with oxygen, the coefficients indicate the specific ratio of molecules required to produce the resulting carbon dioxide and water.2

Mass and the Mole

Because chemists work with weighable quantities, stoichiometry utilizes the concept of the mole. One mole represents a specific number of particles—Avogadro’s number—allowing for the calculation of mass relationships between reactants and products. If a reaction involves a limiting reagent, stoichiometry identifies which substance will be consumed first, thereby determining the maximum amount of product that can be formed.2