Hess's law of heat of summation is based on law of conservation of energy. It has found significance in deriving heats of many reactions which either do not take place or if take place, than other side reactions also accompany it. For example heat of reaction for C + (1)/(2) O_(2) toCO can not be studied directly as it occurs with simultaneous reaction of oxidation of CO to CO_(2). Bond energy is referred as heat enthalpy when a bond is broken to produce isolated gaseous atoms. In case of breaking up of bonds between unlike atoms e.g., C – H bond in CH_(4), bond energy is referred as average bond energy as four C – H bonds are broken up. Which of the following statements are correct : (1)The dissociation of bond is always endothermic (2) The formation of a bond is always exothermic. (3)Heat of formation of an atom = (1)/(2)xx bond energy like atoms covalent bond (4) The heat enthalpy change in a chemical reaction is equal but opposite to the heat enthalpy if reaction is reversed. (5) Hess's law can be verified experimentally.