The law of conservation of mass is a fundamental principle of chemistry and physics stating that in a closed system, mass cannot be created or destroyed during a chemical reaction. This principle dictates that the total mass of the reactants must exactly equal the total mass of the products formed. This concept forms the basis of stoichiometry, allowing scientists to accurately predict the amount of substance that will be consumed or produced during a transformation. The law emphasizes that while matter can change state or react into new compounds, the total quantity of mass remains invariant, providing a core quantitative framework for analyzing chemical changes across various scientific fields.