Final answer:
The principle that the total mass of reactants equals the total mass of products in a chemical reaction is the law of conservation of mass, indicating that mass is conserved during chemical reactions.
Step-by-step explanation:
The principle demonstrated by the fact that the total mass of reactants equals the total mass of products in a chemical reaction is known as the law of conservation of mass. This fundamental principle of chemistry states that mass is neither created nor destroyed in a chemical reaction. In other words, the mass of the substances before the reaction (the reactants) is always equal to the mass of the substances after the reaction (the products).
During a chemical reaction, the atoms of the reactants rearrange to form new substances, which are the products. According to the law of conservation of mass, the sum of the mass numbers of the reactants must equal the sum of the mass numbers of the products. This is true for both the mass and the atomic level, where the sum of the charges of the reactants also equals the sum of the charges of the products.
In an experiment, if you measure the total mass at the start and at the end of a reaction, you would find them to be the same, supporting the concept that mass does not appear or disappear, it is simply conserved during the reaction.