Final answer:
Energy is required to break chemical bonds (endothermic process) and released when new bonds are formed (exothermic process). The bond energy, which is indicative of how much energy is required or released, depends on the strength of the specific bond. The enthalpy change in a reaction indicates the net energy exchange, following the conservation of energy principle.
Step-by-step explanation:
- When bonds are broken energy is required, and when new bonds form energy is released. The energy involved is dependent on the specific chemical bonds. For example, breaking and forming the bond in a hydrogen molecule (H-H) requires and releases the same amount of energy, which is 4.52 eV. This energy is the bond energy.
- Bond breaking is an endothermic process, it absorbs energy. Conversely, bond-making or bond formation is an exothermic process, which releases energy, often in the form of heat. Chemical reactions often involve both bond breaking and bond-making, leading to a net energy change depending on the strength of the bonds involved. If the new bonds are stronger than the bonds broken, energy will be released overall.
In summary, the enthalpy change or heat of reaction indicates whether a reaction overall absorbs or releases energy, adhering to the law of conservation of energy. In the human body, for instance, chemical reactions involve the conversion of chemical energy from food substances into kinetic energy that cells use to perform various functions.