Which best describes the law of conservation of mass? The coefficients in front of the chemicals in the reactants should be based on the physical state of the products. Products in the form of gases are not considered a part of the total mass change from reactants to products. When reactants contain both a solid and a liquid, the solid counts toward the overall mass and the liquid does not. The mass of the reactants and products is equal and is not dependent on the physical state of the substances.