According to the law of conservation of mass, mass can be neither created nor destroyed in a chemical reaction. This means the total mass of the starting materials (reactants) must be equal to the total mass of the ending materials (products).

In a chemical equation, the reactants and products are represented by their chemical formulas. The coefficients in front of the formulas represent the relative number of molecules or moles of each substance involved in the reaction.

If a chemical equation is not balanced, it does not satisfy the law of conservation of mass. This means that either some mass has been lost or gained in the reaction, which is impossible.

Therefore, chemical equations must be balanced to ensure that the law of conservation of mass is satisfied.