Bond energy also known as bond enthalpy is the measure of bond strength in a chemical bond. IUPAC defines bond energy as the average value of the gas-phase bond dissociation energies (usually at 298 K) for all bonds of the same type within the same chemical species. When atoms combine to make a compound, energy is always given off, and the compound has a lower overall energy. When atoms bond together to form compounds they attain lower energies than they would possess as individual atoms. Heat, equal to the difference between the energies of the bonded atoms and the energies of the separated atoms, is released. Thus, the bonded atoms have a lower energy than the individual atoms do. When a bond is strong, there is a higher bond energy because it takes more energy to break a strong bond. This correlates with bond order and bond length. When the Bond order is higher, bond length is shorter, and the shorter the bond length means a greater the Bond Energy because of increased electric attraction. In general, the shorter the bond length, the greater the bond energy. The exact value of a C–H bond energy will depend on the particular molecule, all C–H bonds have a bond energy of roughly the same value because they are all C–H bonds. It takes approximately 100 kcal of energy to break 1 mol of C–H bonds, so the bond energy of a C–H bond is approximately 100 kcal/mol. A C–C bond has an approximate bond energy of 80 kcal/mol, whereas a C=C has a bond energy of about 145 kcal/mol. In order to calculate a more general bond energy find the average of the bond energies of a specific bond in different molecules to get the average bond energy.