Hi, My Modern Physics lecturer is of the opinion that the energy dissipated during exothermic reactions is due to infinitesimally small change in mass of the reactants. Similarly, he said that an infinitesimally small part of the food we eat gets converted into the energy using which we perform mechanical actions. The amount of mass transformed into energy can be calculated using E=Mc2. I argued that this is not possible for ordinary Chemical/ Biological reactions to exhibit Mass to Energy conversion phenomenon governed by E=Mc2. I said that the energy dissipated in these reactions is because of enthalpy change, so the bond energy is converted into heat and other forms. I also said that in such reactions mass of the reactants is equal to the mass of products. I maintained that the only reaction by which we can convert Mass directly into Energy is the Fusion reaction. How valid is either mine or my instructor's argument?