Total bond energy

A/14 the enthalpy of reaction, which is in this case twice the enthalpy of formation of hydrogen chloride. Clearly A/14 is the difference between the total bond energies of the products and the total bond energies ol the reactants, lhat is... 

Table I.IS gives total bonding energies in kilocalories per mole for some simple molecules. The B3iyP results are comparable in accuracy to G1 and G2 results. Another comparison was done with a series of cyclic hydrocarbons as the test case. The calculations were done using an isodesmic reaction scheme. The results are given in Table 1.19. Density functional calculations have also been successfully extended to functionalized molecules. ...

In Fig. 9.1, orbitals below the dashed reference line are bonding orbitals when they are filled, the molecule is stabilized. The orbitals that fall on the reference line are nonbonding placing electrons in these orbitals has no effect on the total bonding energy of the molecule. The orbitals above the reference line are antibonding the presence of electrons in these orbitals destabilizes the molecule. The dramatic difference in properties of cyclobutadiene (extremely unstable) and benzene (very stable) is explicable in terms of... 

Enthalpy change, AH (Section 5.7) The heat of reaction. The enthalpy change that occurs during a reaction is a measure of the difference in total bond energy between reactants and products. 

Method of Craven [50] This average bond energy summation method (ABES) is a simplification of the method described by Sanderson [55]. The reaction enthalpy is calculated by subtracting the total bond energies present before the reaction from the total bond energies of the products. 

TABLE 2.3. Energy Contributions to the Total Bonding Energy (kcal/mol) for Classical Hydrogen-Bonded Complexes Formed by an HNO Molecule"... 

THE NATURE OF DIHYDROGEN BONDING THE TOPOLOGY OF ELECTRON DENSITY AND CONTRIBUTIONS TO TOTAL BONDING ENERGY... 

D// of the above reaction = (Total bond energies of the reactants)... 

As a summary of the results reported above, the bond in the hydrogen molecule may be described as resulting in the main from the resonance of the two electrons between the two nuclei, this phenomenon contributing 80 percent of the total bond energy. An additional 5 percent is contributed by the ionic structures H H+ and H+H , which are of equal importance. The remaining 15 percent of the energy of the bond can be ascribed to complex interactions included under the term deformation.11... 

For a further discussion of ionic versus covalent bonding and the total bond energy resulting from the sum of the two, see Chapter 9, Electronegativity and Hardness and Softness."... 

I8.lt> The P4 molecule in white phosphorus has extremely strained bonds The bond angles in the Tj molecule are only 60°. Therefore the bonds are weak, only 201 kJ mol-1 for each one. The total bond energy of two moles of Pj (962 kJ. Appendix E)is244 kJ less than that of one mole of Pi (1206 kJ. Appendix E). In contrast, the total bond energy of two moles of N. has been calculated57 to be 77 kJ greater than that of one mole of N, ta hypothetical tetrahedral molecule iscslraclund with P4)... 

Oog and Hunt8711 found the heat of combustion of ethylene oxide to be 312 55 0.20 koal./mole. The heats of fusion and vaporization, determined with great precision by Giauque and Gordon,8 8 are 1236 and 6101 kcal./moie respectively. An approximate value for the strain energy of ethylene oxide has been computed by Nelson and Jeesup.mv The experimental heat of formation, derived by combustion calari-> metry, was subtracted from the calculated total bond energy, obtained... 

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