The principle of conservation of mass states that mass in a closed system cannot be created or destroyed; it can only change forms. This principle suggests that during a chemical reaction, the total mass of the reactants is equal to the total mass of the products. It forms a foundational concept in both chemistry and physics, emphasizing that matter is conserved in all physical and chemical processes. This principle supports the understanding of chemical reactions, allowing scientists to predict outcomes and balance equations in a systematic manner.