law of conservation of mass

basic law of nature which claims that mass is neither created nor wasted but rather changes form

The law of conservation of mass/matter, also known as law of mass/matter conservation (or the Lomonosov-Lavoisier law), states that the mass of a closed system will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter cannot be created/destroyed, although it may be rearranged. 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.
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Noun
1. a fundamental principle of classical physics that matter cannot be created or destroyed in an isolated system
(synonym) conservation of mass, conservation of matter, law of conservation of matter
(hypernym) conservation

There is no change in total mass during a chemical change. The demonstration of conservation of mass by Antoine Lavoisier in the late 18th century was a milestone in the development of modern chemistry.