Binding energy

Binding energy is the energy required to disassemble a whole system into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts; this is what keeps the system together. Often this means that energy is released upon the creation of a bound state. This definition corresponds to a positive binding energy.

In general, binding energy represents the mechanical work that must be done against the forces which hold an object together, disassembling the object into component parts separated by sufficient distance that further separation requires negligible additional work.

In bound systems, if the binding energy is removed from the system, it must be subtracted from the mass of the unbound system, simply because this energy has mass. Thus, if energy is removed (or emitted) from the system at the time it is bound, the loss of energy from the system will also result in the loss of the mass of the energy from the system. System mass is not conserved in this process because the system is "open" (i.e., is not an isolated system to mass or energy input or loss) during the binding process.

There are several types of binding energy, each operating over a different distance and energy scale. The smaller the scale of a bound system, the higher its associated binding energy.

In astrophysics, the gravitational binding energy of a celestial body is the energy required to expand the material to infinity. Solely for the purpose of comparison with the other types of binding energy, if a body with the mass and radius of the Earth were made purely of carbon-12, then the gravitational binding energy of that body would be about 4.66 eV per atom. If a carbon-12 body had the mass and radius of the Sun, its gravitational binding energy would be about 14.24 keV per atom.

At the molecular level, bond energy and bond-dissociation energy are measures of the binding energy between the atoms in a chemical bond. It is the energy required to disassemble a molecule into its constituent atoms. This energy appears as chemical energy, such as that released in chemical explosions, the burning of chemical fuel and biological processes. Bond energies and bond-dissociation energies are typically in the range of few eV per bond. For example, the bond-dissociation energy of a carbon-carbon bond is about 3.6 eV.

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