Gibbs Energy Calculations

This is a 4 2 reaction, and is thus pressure dependent. However, it is necessary to compute the equilibrium partial pressure of some alternative gaseous species, such as SiCls, and other hydrocarbons such as C2H2 and for this a Gibbs energy minimization calculation should be made. 

As shown in [30], the maximum achievable efficiency of solar-to-chemical energy conversion (calculated with respect to Gibbs free energy) is ca. 60% for the thermocatalytic method and ca. 30% for the photocatalytic method. 

The excess Gibbs energy GE calculated from a liquid phase activity coefficient model, and the excess Gibbs energy GE calculated from the equation-of-state are equal at infinite pressure ... 

In water solution, as shown by AMSOL calculations, the conformational preferences of the studied amides show up. Gibbs free energies ofhydratation calculated with the SM5.4 model and PM3 hamiltonian for structures optimized at the RHF/6-3 1G level indicated that those most favored by hydratation are the T- and G-conformers for the diamide and A, A,A ,A -tetramethyldiamide of (R, R (-tartaric acid, respectively. 

Optimized geometries, potential energies, Gibbs free energies, and vibrational frequencies were calculated for all possible tautomers of triphospholes and tetraphosphole molecules at the B3LYP/aug-cc-pVTZ level (Figure 2)... 

IR spectra, total energy, Gibbs free energy, and the highest n and c electronic states calculated for tautomers of 5-substituted imidazoles by ab initio (MP2, RHT/6-311++G ) show that such substituents as N02, NH2, CN, etc. stabilize the N3-H tautomer more [1042], Therefore the conclusions derived from these data are related to molecules in the gas state and cannot be extended to the imidazoles in the solvated state. 

The Gibbs free energy is calculated from the equation... 

The boiling point is calculated from the adopted thermodynamic functions and the chosen enthalpy of sublimation at 298.15 K so that the Gibbs energy functions calculated by integration of the crystal liquid data and by statistical methods from the gas phase are equal at the boiling point. 

At the boiling point and higher temperatures sodium vapor contains an appreciable proportion of diatomic moleculses. Thompson and Garelis (j ) have made a careful analysis of the available vapor pressure data. Their results are consistent with the Gibbs energy functions calculated in the present work and have been adopted. 

As Table 1.1 shows, fluorine is the second smallest element, with size approximately 20% larger than the smallest element, hydrogen. Table 1.2 summarizes four steric parameters for various elements and groups (i) Taft steric parameters Es [44], (ii) revised Taft steric parameters E [45], (iii) Charton steric parameters o [46], and (iv) A values [47], The steric parameters, Es, E, and u are determined on the basis of relative acid-catalyzed esterification rates, while the A values are derived from the Gibbs free energy difference calculated from the ratios of axial and equatorial conformers of monosubstituted cyclohexanes by NMR. 

Chemical equilibrium for a reaction is associated with the change in Gibbs free energy (AGr) calculated as follows ... 

Figure 6.2.1. Excess Gibbs free energy and excess enthalpy of the acetone and water binary mixture at 293 K. The excess Gibbs free energy was calculated from VLE data as described in Section 5.1, The excess enthalpy data are as reported in the DECHEMA Chemistry Data Series Heat of Mixing Collection, Christiansen et al. 19S4, Vol, l,Pt. lb, pp. 148-9.

The Gibbs activation energy is calculated from equation (7.4.15) ignoring the activity coefficients. From equation (7.4.20) the rate constant at 25°C is 1.82 X 10 M s . Thus,... 

The authors also evaluated the enthalpy of the dimerisation reaction 2SnSe(g) Sn2Sc2(g) to be A,// (298.15 K) = -(194.6 + 22.0) kJ-mol in a third law analysis of measurements made in the temperature range 936 to 991 K.. No evaluation was made according to the second law because of the short temperature range. The third law evaluation employed Gibbs energy functions calculated from parameters estimated by comparison with the isoelectronic molecules As4(g) and Sb4(g). In the absence of better values of the molecular parameters, no recalculation was made by the review. 

Enthalpies of formation at 0 K for the species Se2(g)-Seg(g) were derived using Gibbs energy functions calculated from estimated molecular parameters. In the present review, the experimental results presented in Tables 11 and 15 to 20 of the paper were re-evaluated using the second and third laws and the selected data for the heat capacities and entropies. The results are summarised in the Table A-78. No evaluation using the second law can be made for Se4(g) because the measurements were made at a single temperature only. 

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