Chemical equations must be balanced according to the law of conservation of mass because this fundamental principle states that during any physical or chemical change, the total mass of the reactants must equal the total mass of the products. In a chemical equation, this means that the number of atoms of each element present on the reactant side of the equation must exactly match the number of atoms of these same elements present on the product side. Balancing a chemical equation ensures that this mass balance is maintained and that the reaction adheres to the law of conservation of mass. The balanced equation allows us to accurately predict the quantitative relationships between the reactants and products involved in the reaction. By balancing equations, we ensure that the chemical transformations can be correctly described and studied, providing a robust basis for accurate chemical calculations and insights into the stoichiometry of chemical reactions.