“Nothing comes from nothing” is an important idea in ancient Greek philosophy that argues that what exists now has always existed since no new matter can come into existence where there was none before. Antoine Lavoisier (1743-1794) restated this principle for chemistry with the law of conservation of mass, which “means that the atoms of an object cannot be created or destroyed, but can be moved around and be changed into different particles.”
This law says that when a chemical reaction rearranges atoms into a new product, the mass of the reactants (chemicals before the chemical reaction) is the same as the mass of the products (the new chemicals made). More simply, whatever you do, you will still have the same amount of stuff (however, certain nuclear reactions like fusion and fission can convert a small part of the mass into energy.
The law of conservation of mass states that the total mass present before a chemical reaction is the same as the total mass present after the chemical reaction; in other words, mass is conserved. The law of conservation of mass was formulated by Lavoisier as a result of his combustion experiment, in which he observed that the mass of his original substance—a glass vessel, tin, and air—was equal to the mass of the produced substance—the glass vessel, “tin calx”, and the remaining air.
The law of conservation of matter summarizes many scientific observations about the matter:
It states that there is no detectable change in the total quantity of matter present when matter converts from one type to another (a chemical change) or changes among solid, liquid, or gaseous states (a physical change).
This is really a consequence of “conservation of atoms” which are presumed to be indestructible by chemical means. In chemical reactions, the atoms are simply rearranged but never destroyed.
Mass conservation had special significance in understanding chemical changes involving gases, which were for some time not always regarded as the real matter at all. Owing to their very small densities, carrying out actual weight measurements on gases is quite difficult to do, and was far beyond the capabilities of the early experimenters.
Thus when magnesium metal is burned in air, the weight of the solid product always exceeds that of the original metal, implying that the process is one in which the metal combines with what might have been thought to be a “weightless” component of the air, which we now know to be oxygen.