CONCEPTS

Matter Conservation Law

We explain what is the law of conservation of matter or Lomonósov-Lavoisier Law. History, background and examples.

  1. Matter Conservation Law

The law of conservation of matter, also known as the law of conservation of mass or simply as the law Lomonósov-Lavoisier (in honor of the scientists who postulated it), is that principle of chemistry that states that matter is not created or It is destroyed during a chemical reaction , it only transforms.

This means that the quantities of the masses involved in a given reaction must be constant throughout it, that is, they will not have changed in their proportions when the reaction ends, although they may have been transformed.

This fundamental principle of the natural sciences was postulated by two scientists simultaneously and independently: the Russian Mikhail Lomonosov in 1748 and the Frenchman Antoine Lavoisier in 1785. It is striking that this occurred before the discovery of the atom and the postulation of atomic theory , with which it is much simpler to explain and illustrate the phenomenon.

The exception to the rule is nuclear reactions , in which it is possible to convert mass into energy and vice versa, being able to “create” and “destroy” them for convenience, even if matter is really being transformed into energy and vice versa.

Along with the equivalence between mass and energy, the law of conservation of matter was key to the understanding of contemporary chemistry.

  1. Background of the Law of conservation of matter

The chemistry of those years understood the reaction processes very differently from the current one, in some cases coming to affirm the contrary to what this law raises.

Robert Boyle’s experiments in the seventeenth century , weighing different metals before and after allowing them to oxidize, attributed the change in weight to the gain of matter, ignoring that rust meant the extraction of oxygen atoms from the air by the metal.

  1. Discovery of the Law of conservation of matter

The experiences that led Lavoisier to the discovery of this principle have to do with one of the main interests of the chemistry of the time, such as combustion. By heating various metals, the French realized that they gained mass when calcined if they were left exposed to the air, but that their mass remained identical if they were in closed containers.

Thus, he deduced that this extra amount of mass came from somewhere, and he could propose his theory that it was not created, but taken from the air . Therefore, under controlled conditions, the amount of reagent mass before the chemical process and the amount of subsequent mass can be measured , and the nature of the products must necessarily be identical .

  1. Example of the Law of conservation of matter

A perfect example of this law is the combustion of hydrocarbons , in which the fuel can be seen burning and “disappearing”, when in truth it will have been transformed into invisible gases and released energy.

For example, when burning methane (CH 4 ) we will have the following reaction, whose by-products will be gaseous and invisible, but of an identical amount of atoms:

CH 4 + 2O 2 (from air) CO 2 + 2H 2 O (water vapor) + energy

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