Exothermic is bond making.. Endothermic is bond breaking. Bond making is exo because the the new product has to get rid the extra energy to be stable. The energy is lost to the surroundings. Energy diagram for exo reactions shows the energy of the products is lower than thr reactant.. This is because the reactants have lost energy and the products will have low amounts of energy ... Energy diagrams shows the energy of the reaction only, if more bonds are formed than being broken, it is an exo process and vice versa.