The total mass of the reactants is equal to the total mass of the products due to the law of conservation of mass.
The law of conservation of mass states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. This principle is based on the idea that atoms are neither created nor destroyed during a chemical reaction; they are rearranged to form new substances. In the case of the reaction between substance X and substance Y, which results in the formation of four molecules of the same compound, the total mass of the reactants (X and Y) must be equivalent to the total mass of the products.
Chemical reactions involve the breaking and forming of chemical bonds, but the total number and types of atoms on both sides of the reaction remain unchanged. As a result, the mass before the reaction must be equal to the mass after the reaction. This conservation of mass is a fundamental principle in chemistry and is crucial for understanding and predicting the outcomes of chemical reactions. Therefore, in the given scenario, the total mass of the reactants is equal to the total mass of the products due to the law of conservation of mass.