The law of conservation of mass states that in a closed system, the total mass remains constant during a chemical reaction. This fundamental principle, proposed by Antoine Lavoisier in the late 18th century, asserts that atoms are neither created nor destroyed in a chemical reaction; they are rearranged to form new substances. The total mass of the reactants equals the total mass of the products. This law underpins the foundation of modern chemistry, providing a crucial understanding of the preservation of matter in chemical processes and serving as a fundamental principle in balancing chemical equations.