If for some reason the energy supply stops they will become a closed system and fail. All open systems will eventually fail due to the process of energy turning into useless heat. The universe will eventually die due to a lack of useful energy and an abundance of heat. The universe is a closed system. Covalent bonds contain the most energy,while hydrogen bond much less.
Energy is released when new bond are formed.
This is called bond energy. Always subtract the product answer from the reactant answer. If a reaction has a negative delta H, it is said to be exothermic. The total potential energy of a molecule. Enthalpy relates to the amount of heat energy released from a chemical reaction.