Thermochemical bond energy Definition

Energy characteristics of atoms also define, to a large extent, the strengths of their bonds in molecules, polyatomic ions and radicals. The work required to disrupt a chemical bond, e.g. to separate chemically bonded atoms from the equilibrium distance to a practically infinite one (in the ground state) is called bond energy Eb). In case of the A2 and AX molecules, Eb is equal to the dissociation energy of the molecule (De) which can be determined by thermochemical, calorimetric, kinetic, mass-spectroscopic and molecular spectroscopic techniques. By definition, De characterizes atoms in molecules at the equilibrium state with zero-point energy,... 

A modified definition of resonance energy has been introduced by Dewar (66T(S8)75, 69JA6321) in which the reference point is the corresponding open-chain polyene. In principle this overcomes the difficulties inherent in comparing observed stability with that of an idealized molecule with pure single and double bonds, as thermochemical data for the reference acyclic polyenes are capable of direct experimental determination. In practice, as the required data were not available, recourse was made to theoretical calculations using a semiempirical SCF-MO method. The pertinent Dewar Resonance Energies are listed in Table 30. 

According to the multiplet theory the energy Eab.k which should be spent to break the bond A—B into atoms adsorbed by the catalyst will not be equal to Qab now. According to the definition we have the thermochemical equation... 

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