A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants, which are the starting substances, on the left side and the products, which are the substances formed, on the right side. The reactants and products are separated by an arrow that indicates the direction of the reaction. In a balanced chemical equation, the number of atoms for each element is the same on both sides, following the law of conservation of mass. This ensures that matter is neither created nor destroyed during the reaction. For example, in the equation for the combustion of methane, CH4 + O2 → CO2 + H2O, CH4 and O2 are the reactants, while CO2 and H2O are the products.