Bond energy average values

Tabulated bond energies are generally values of bond energies averaged over a number of selected typical chemical species containing that type of bond. 

For many purposes, for example the estimation of approximate heats of formation (p. 63), it is sufficient to have an average value. This average of the bond dissociation energies is called the average thermochemical bond energy or (more commonly) simply the bond energy. ... 

Strictly, these values are bond enthalpies, but the term energies is commonly used. Other descriptions are average standard bond energies, mean bond energies . 

Extensive reviews of the effects of fluonnation on stmeture and bonding are available [75, 76, 77], and only the charactenstic trends in bond strengths will be covered here. The bond energies cited are average values corrected for the revised heats of formation of alkyl radicals [78], but their precision is seldom better than 2 kcal/mol for the fluoro compounds. 

Tables 2.3 and 2.4 list a selection of typical dissociation energies. The values given in Table 2.4 are average dissociation energies for a number of different molecules. For instance, the strength quoted for a C—O single bond is the average strength of such bonds in a selection of organic molecules, such as methanol (CH3—OH), ethanol (CH,CH2—OH), and dimethyl ether (CH,—O—Cl l5). The values should therefore be regarded as typical rather than as accurate values for a particular molecule.

Neglecting the possibility that the bond energy in primary amines be slightly less than in secondary and tertiary amines, we take the average value 2.88 v. e. for C N. 

Now we apply Equation, using average bond energy values from Table 6-2 - reaction — / j -S - bondsbroken - bonds formed A table helps us... 

The AH factor for the change can be equated with the difference in energies between the bonds in the starting materials and the bonds in the products, and an approximate value of AH for a reaction can often be predicted from tables of standard bond energies which is hardly unexpected, as it is from AH data that the average bond energies were compiled in the first place ... 

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