According to the law of consservation of mass, how does the mass of the products in a chemical reaction compare to the mass of the reactants?

The mass of products is comparatively less as some of the mass is converted into heat

According to the law of conservation of mass, mass can neither be created nor destroyed but it can only be converted from one form to another. Since mass can also be converted to energy according to the equation E=mc² then in a chemical reaction some amount of reactanats mass is converted into heat energy to carry out the reaction and hence the amount of products is slightly less.