Conservation of mass
![Russian scientist Mikhail Lomonosov discovered the law of mass conservation in 1756 by experiments, and came to the conclusion that phlogiston theory is incorrect.[1][2][3]](/Images/godic/202502/04/M.V._Lomonosov_by_L.Miropolskiy_after_G.C.Prenner_(1787,_RAN)5427.jpg")
![Antoine Lavoisier's discovery of the Law of Conservation of Mass led to many new findings in the 19th century. Joseph Proust's law of definite proportions and John Dalton's atomic theory branched from the discoveries of Antoine Lavoisier. Lavoisier's quantitative experiments revealed that combustion involved oxygen rather than what was previously thought to be phlogiston.](/Images/godic/202502/04/Antoine_laurent_lavoisier5427.jpg")
The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time. The law implies that mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work had contributed. The law implies (requires) that during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products.