The nature of bonding in hexahalothorates and hexahalouranates(IV)

1983 ◽  
Vol 61 (7) ◽  
pp. 1573-1577 ◽  
Author(s):  
Alan D. Westland ◽  
M. T. H. Tarafder
Keyword(s):  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Bond Energies ◽  
Standard Enthalpies Of Formation ◽  
Lattice Energies ◽  
Semi Empirical

Enthalpies of reaction have been determined by solution calorimetry for the process 2AX(c) + ThX4(c) = A2ThX6(c) where A = K, Cs and X = Cl, Br. The measurements afforded the following values of standard enthalpies of formation [Formula: see text], in kJ mol−1: K2ThCl6, −2108; Cs2ThCl6, −2151; K2ThBr,−1774; Cs2ThBr6,−1826. The standard enthalpies of formation of ThCl62− (g), ThBr62− (g), UCl62− (g), and UBr62− (g) and the two-halide ion affinities of ThCl4, ThBr4, UCl4, and UBr4 were compared by assuming semi-empirical (Kapustinskii) values of the lattice energies of the complexes. Homolytic and heterolytic bond energies were also calculated.

Bond Energies

2008 ◽  
Author(s):  
José A. Martinho Simões ◽  
Manuel Minas da Piedade
Keyword(s):  
Driving Forces ◽  
Theoretical Models ◽  
Enthalpies Of Formation ◽  
Chemical Bonds ◽  
Bond Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Or Groups ◽  
Quantum Chemistry Calculations ◽  
Standard Enthalpies Of Formation

Although standard enthalpies of formation provide information about the net stability of molecules and their transformations, they do not always indicate stability of individual bonds. This analysis normally involves parameters, loosely called “bond energies,” that reflect the amount of energy required to cleave chemical bonds. Bond energies are essential for understanding the nature of chemical bonds. They can be used to assess the results from quantum chemistry calculations (or from other, less sophisticated theoretical models) and thus support or oppose the descriptions of those bonds. Moreover, bond energy values also enable us to estimate the driving forces of chemical reactions by considering the strengths of all the bonds that are cleaved and formed. In fact, there are many reactions for which the standard enthalpies of formation of all reactants and products are not available (and cannot be easily estimated) but whose energetics can be predicted from the appropriate bond energies. In the previous chapters, we attempted to review all the important parameters in molecular energetics, but to avoid unnecessary distraction, we deliberately omitted bond energies from the discussion. The literature is plagued with a variety of concepts that fall into that designation but are not always synonymous. We can find names like bond strengths, bond enthalpies, bond energies, bond dissociation enthalpies, bond dissociation energies, bond disruption enthalpies, bond enthalpy terms, intrinsic bond energies, and symbols like D, D̄, 〈D〉, E, BDE, and so on. The meaning of these concepts it not always obvious and, unfortunately, some are occasionally misused. Now we look into each one of them. Consider a molecule AB, where A and B can be atoms or groups of atoms.

scholarly journals Enthalpies of formation of lanthanide oxyapatite phases

2001 ◽  
Vol 16 (10) ◽  
pp. 2780-2783 ◽  
Author(s):  
A. S. Risbud ◽  
K. B. Helean ◽  
M. C. Wilding ◽  
P. Lu ◽  
A. Navrotsky
Keyword(s):  
Structural Formula ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Enthalpies Of Solution ◽  
Thermodynamic Cycles ◽  
Oxide Melt ◽  
Formation Enthalpies ◽  
High Temperature Oxide ◽  
Standard Enthalpies Of Formation ◽  
Temperature Oxide

A family of lanthanide silicates adopts an oxyapatitelike structure with structural formula Ln9.33 0.67(SiO4)6O2 (Ln = La, Sm, Nd, Gd,   = vacancy). The enthalpies of solution, ΔHS, for these materials and their corresponding binary oxides were determined by high-temperature oxide melt solution calorimetry using molten 2PbO B2O3 at 1078 K. These data were used to complete thermodynamic cycles to calculate enthalpies of formation from the oxides, ΔH0 f-oxides (kJ/mol): La9.33 0.67(SiO4)6O2 = 776.3 ± 17.9, Nd9.33 0.67(SiO4)6O2 = 760.4 ± 31.9, Sm9.33 0.67(SiO4)6O2 = 590.3 ± 18.6, and Gd9.33 0.67(SiO4)6O2 = 446.9 ± 21.9. Reference data were used to calculate the standard enthalpies of formation from the elements, ΔH0 f (kJ/mol): La9.33 0.67(SiO4)6O2 = 14611.0 ± 19.4, Nd9.33 0.67(SiO4)6O2 = 14661.5 ± 32.2, Sm9.33 0.67(SiO4)6O2 = -14561.7 ±; 20.8, and Gd9.33 0.67(SiO4)6O2 = -14402.7 ± 28.2. The formation enthalpies become more endothermic as the ionic radius of the lanthanide ion decreases.

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