Chemistry: conservation of mass

Tutoring chemistry, there are fundamental laws. The tutor mentions conservation of mass.

The Law of Conservation of Mass states that the total mass of the reactants – or inputs – of a reaction will equal the total mass of the products, or outputs. Most people probably have a fairly easy time believing it, nowadays; when Lavoisier stated it in the late 1700s, it perhaps wasn’t as obvious to everyone.

Modern chemistry, it seems, has made this idea a bit more specific: not only will the total mass of the products match that of the reactants, but the total mass of each element found among the products will match its total mass on the reactant side. This allows chemists to predict outputs based on inputs, since a given reaction may have numerous outputs, but only one of particular interest.

The Law of Conservation of Mass predates modern atomic theory.

Source:

chem.libretexts.org