主题：【原创】听我来上科学课 -- 月色溶溶

The law of conservation of mass/matter, also known as law of mass/matter conservation, states that the mass of a closed system of substances will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter cannot be created nor destroyed, although it may change form. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products. The law of mass/matter conservation may be considered as an approximate physical law that holds only in the classical sense before the advent of special relativity and quantum mechanics.