Balancing an equation means adjusting the stoichiometric coefficients so that the number of atoms of each element is equal on both sides of the reaction arrow. This is required because the law of conservation of mass demands that no atoms are created or destroyed in a chemical reaction. Only the coefficients may be changed in balancing; the chemical formulas themselves must not be altered.

配平方程式是指调整化学计量系数,使反应箭头两侧每种元素的原子数目相等。这是必需的,因为质量守恒定律要求化学反应中不产生也不消灭原子。配平时只能改变系数,而绝不能更改化学式本身。