The Law of Conservation of Mass states that mass cannot be created or destroyed in a closed system during a chemical reaction. This means that the total mass of the reactants before the reaction is equal to the total mass of the products after the reaction. This principle was formulated by the chemist Antoine Lavoisier in the 18th century and is fundamental to the study of chemistry. In practical terms, when substances undergo a chemical change, such as burning or reacting, the atoms rearrange to form new substances, but the overall mass remains constant. This law is crucial for balancing chemical equations, ensuring that the same number of each type of atom is present on both sides of the equation.