The law of conservation of mass states that in a closed or isolated system, matter cannot be created or destroyed; it can only change forms. This means that during a chemical reaction, the total mass of the products is equal to the total mass of the reactants
. Essentially, the mass of an object or collection of objects remains constant regardless of how the parts rearrange themselves
. This principle was first clearly documented by Antoine Lavoisier in the late 18th century, who showed through meticulous experiments that mass is conserved in chemical reactions. It laid the foundation for modern chemistry by proving that substances do not simply disappear but transform into other substances of equal mass
. Mathematically, in classical mechanics and fluid dynamics, the conservation of mass is expressed by the continuity equation, which states that the rate of change of mass within a volume plus the net flow of mass across its boundary is zero. This ensures that the total mass in an isolated system remains constant over time
. However, the law is an approximation that holds true under classical conditions. In nuclear reactions and high-energy physics, mass can be converted to energy and vice versa, as described by Einstein’s mass-energy equivalence principle. Thus, in such cases, the more general conservation of mass-energy applies rather than strict conservation of mass alone
. In summary:
- Matter cannot be created or destroyed in chemical reactions; total mass remains constant.
- The law applies strictly to closed or isolated systems.
- It was established by Antoine Lavoisier in the 18th century.
- The law is fundamental to chemistry and is expressed mathematically by the continuity equation.
- At very high energies or in nuclear processes, mass can convert to energy, requiring a broader conservation law of mass-energy.
This principle explains why chemical equations must be balanced to reflect that atoms (and thus mass) are conserved during reactions
