Bond Dissociation Enthalpies and Energies

Consider a molecule AB, where A and B can be atoms or groups of atoms. The A-B bond dissociation enthalpy, represented by DH (A-B), is defined as the standard enthalpy of the gas-phase reaction where the only event is the cleavage of that bond at a given temperature  

The A-B bond dissociation energy, on the other hand, is the standard internal energy of reaction 5.1. It is abbreviated by DUf(A-B) and its relation with DHj A-B) is given by 

As stated in section 2.2, the subscript T will be omitted whenever the temperature refers to 298.15 K. In this case, 

There are numerous publications where the standard enthalpy of reaction 5.1 is calledbond dissociation energy and abbreviated by BDE or by (A-B). However, this designation (as well as the abbreviations) can be misleading, and we favor the nomenclature just indicated. It should also be recalled (see section 2.2) that the International Union of Pure and Applied Chemistry (IUPAC) recommends Do for the dissociation energy at T = 0 (therefore, Do = DUfi = DH ) and De for the hypothetical dissociation energy from the potential minimum [13], 

Bearing in mind that a bond dissociation enthalpy is simply the standard enthalpy of a particular reaction, the relationship between two values of )//) ( A B) at different temperatures is easily obtained as 

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