Bond Energy

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bond energy

[′bänd ‚en·ər·jē]
(physical chemistry)
The average value of specific bond dissociation energies that have been measured from different molecules of a given type.

Energy, Bond

 

the work required to break up a molecule into two parts (atoms, groups of atoms) and separate them an infinite distance from each other. For example, when considering the bond energy of H3C—H in a methane molecule, the two parts are the methyl group CH3 and the hydrogen atom H; when considering the bond energy of H—H in a hydrogen molecule, each hydrogen atom constitutes a part.

The bond energy is a specific case of binding energy and is generally expressed in kilojoules per mole (kJ/mole) or kilocalories per mole (kcal/mole). The value of the bond energy ranges from 8–10 to 1,000 kJ/mole, depending on the particles forming the chemical bond, the nature of the interaction between the particles (such as a covalent bond or hydrogen bond), and the multiplicity of the bond (for example, a double or triple bond). For molecules containing two or more identical bonds, the bond energy of each bond (bond dissociation energy) is distinguished from the mean bond energy, which is equal to the averaged value of the dissociation energy of the bonds. For example, the dissociation energy of the HO—H bond in a molecule of water, that is, the heat effect reaction H2O = HO + H, is equal to 495 kJ/mole; the dissociation energy of the H—O bond in a hydroxyl group is equal to 435 kJ/mole, and the mean bond energy is thus equal to 465 kJ/mole. The difference between the values of the bond dissociation energy and the mean bond energy is due to the fact that, during partial molecular dissociation (the breaking of one bond), a change occurs in the electron configuration and in the mutual arrangement of the remaining atoms in the molecule, thereby altering their interaction energy. The value of the bond energy depends on the initial molecular energy, which is sometimes referred to as the temperature dependence of bond energy. The bond energy is usually considered for cases where the molecules are in the standard state or at 0°K. These are the values of the bond energy commonly given in handbooks.

The bond energy is an important characteristic that determines the reactivity of a substance and is used in the thermodynamic and kinetic calculations of chemical reactions. It may be determined indirectly from given calorimetric measurements; it may also be determined by direct calculations and by means of mass spectroscopy and spectral analysis.

REFERENCES

Energiia razryva khimicheskikh sviazei: Potentsialy ionizatsii i srodstvo k elektronu. Moscow, 1974.
Kireev, V. A. Kurs fizicheskoi khimii, 3rd ed. Moscow, 1975.
References in periodicals archive ?
* Extremely high inter-atomic bonding energy (Si - O [right arrow] 0.163 nm; UV wavelength is in the range of 10 to 400 nm).
Table 2 shows that the bonding energy of the unrelaxed interface is smaller than that of the relaxed one, indicating that the relaxed interface is more stable.
The bonding energy of C-H bond of alkanes was higher than that of the C-C bond; therefore, homolysis of thermal pyrolysis started with C-C bond [14, 15], so did DIOS.
The latter corresponds to the bonding energy of [XHal.sub.2] dimers (with changed sign).
Values of differential enthalpy of sorption are higher than the value of latent heat of vaporization of pure water (Figure 1), indicating that the bonding energy between water molecules and sorption sites is higher than the bonding energy among water molecules in liquid phase (Masuzawa & Sterling, 1968).
Atthe same calculation level, the BB bonding energy of -FBBF- is -31.6 kcal/mol, which implies its singlet is not stable.
The low bonding energy component centered at 530.55 eV is attributed to [O.sup.2-] ions on the wurtzite structure of the hexagonal [Zn.sup.2+] ion array, surrounded by Zn atoms with their full complement of nearest neighbor [O.sup.2-] ions [15].
The hydrogen bonding energy ([DELTA]E in kcal/mol) can be empirically calculated by introducing Schaefer's correlation [35], expressed as [DELTA][delta] = (-0.4 [+ or -] 0.2) + [DELTA]E, where [DELTA][delta] is given in parts per million for the difference between chemical shift in the O-H peak of 1 and that in phenol ([delta] 4.29).
While Krupitzer acknowledges that steel isn't the right solution for everything in the production of a vehicle, that a variety of other materials are certainly necessary, he thinks that from an environmental lifecycle point of view, the steel industry is in a good position, not only because many plants have undergone transformations that make them more energy-efficient but because when you get down to the fundamentals, "It is easier to free up iron from iron oxide than aluminum from aluminum oxide because of the bonding energy." Less energy is required in that up-front stage.
Furthermore, the MPC sleeve maximizes transformation of the energy from the water jets into bonding energy thanks to the additional effect of jet rebound.
And the gains in entropy more than compensate for the loss in hydrogen bonding energy.
The signal is independent of temperature variations on the globe, since the hydrogen bonding energy system is already fully occupied at earthly temperatures.