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Law of Conservation of Mass

The law of conservation of mass or of matter, also known as the Lomonosov-Lavoisier law, states that the mass of substances in a closed system will remain constant, no matter what processes are acting inside the system. It is a different way of stating that though matter may change form, it can be neither created nor destroyed. The mass of the reactants must always equal the mass of the products.

This law works fine for anything that is not approaching the speed of light; at high speeds, mass begins transforming to energy (for which reason, we now have the Law of Conservation of Mass and Energy). However, this means that in most situations the law of conservation of mass can be assumed valid.

This law was first formulated by Antoine Lavoisier in 1789, but Mikhail Lomonosov in 1748 had also expressed similar ideas earlier. It was the key to making chemistry into a real science instead of an offshoot of alchemy; prior to this, buoyancy of gases made it difficult to determine before and after measurements of weight. After this, the ideas of chemical elements, process of fire and oxidation, and many other basic chemical principles could be understood.

In nuclear reactions and in very large astronomical objects, this law becomes questionable.

Web Resources On Law of Conservation of Mass

NASA Conservation of Energy
The Conservation Laws of Physics

Book Resources On Law of Conservation of Mass

Systems of Conservation Laws 1 : Hyperbolicity, Entropies, Shock Waves by Denis Serre
Numerical Schemes for Conservation Laws by Dietmar Kröner

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