During a chemical change, which law states that mass is conserved?

The law that states mass is conserved during a chemical change is the Law of Conservation of Mass. This fundamental principle, first formulated by Antoine Lavoisier in the late 18th century, asserts that in a closed system, the total mass of reactants must equal the total mass of products. This means that in any chemical reaction, matter cannot be created or destroyed; it can only change forms. Therefore, when reactants undergo a reaction to form products, the mass of all substances involved remains constant.

Understanding this law is crucial in stoichiometry, where calculations related to the quantities of reactants and products are made. It underpins balanced chemical equations, where the number of atoms for each element is the same on both sides of the equation, reflecting mass conservation in the transformation from reactants to products. This principle allows chemists to predict the outcomes of reactions accurately, ensuring that calculations regarding substances involved in reactions are precise and reliable.