The D values may be easy or difficult to measure, and they can be estimated by various techniques.90 When properly applied, ‘‘Pauling’s original electronegativity equation accurately describes homolytic bond dissociation enthalpies of common covalent bonds, including highly polar ones, with an average deviation of (1.5kcalmol1 [6.3kJmol1] from literature values).’’91 Whether measured or calculated, there is no question as to what D values mean. With E values the matter is not so simple. For methane, the total energy of conversion from CH4 to Cþ4H (at 0K) is 393kcalmol1 (1644kJmol1).92 Consequently, E for the CH bond in methane is 98kcal mol1 (411kJ mol1)at0 K.Themoreusualpractice,though,isnottomeasuretheheatofatomization (i.e., the energy necessary to convert a compound to its atoms) directly but to calculate it from the heat of combustion. Such a calculation is shown in Figure 1.11.
The D values may be easy or difficult to measure, and they can be estimated by various techniques.90 When properly applied, ‘‘Pauling’s original electronegativity equation accurately describes homolytic bond dissociation enthalpies of common covalent bonds, including highly polar ones, with an average deviation of (1.5kcalmol1 [6.3kJmol1] from literature values).’’91 Whether measured or calculated, there is no question as to what D values mean. With E values the matter is not so simple. For methane, the total energy of conversion from CH4 to Cþ4H (at 0K) is 393kcalmol1 (1644kJmol1).92 Consequently, E for the CH bond in methane is 98kcal mol1 (411kJ mol1)at0 K.Themoreusualpractice,though,isnottomeasuretheheatofatomization (i.e., the energy necessary to convert a compound to its atoms) directly but to calculate it from the heat of combustion. Such a calculation is shown in Figure 1.11.
การแปล กรุณารอสักครู่..