Formation, thermodynamic functions enthalpy

Enthalpy of Formation. Thermodynamic Functions Enthalpy of Formation A H in kJ/mol... 

Formation, thermodynamic functions (continued) enthalpy (continued)... 

A general prerequisite for the existence of a stable interface between two phases is that the free energy of formation of the interface be positive were it negative or zero, fluctuations would lead to complete dispersion of one phase in another. As implied, thermodynamics constitutes an important discipline within the general subject. It is one in which surface area joins the usual extensive quantities of mass and volume and in which surface tension and surface composition join the usual intensive quantities of pressure, temperature, and bulk composition. The thermodynamic functions of free energy, enthalpy and entropy can be defined for an interface as well as for a bulk portion of matter. Chapters II and ni are based on a rich history of thermodynamic studies of the liquid interface. The phase behavior of liquid films enters in Chapter IV, and the electrical potential and charge are added as thermodynamic variables in Chapter V. 

Carell and Olin (58) were the first to derive thermodynamic functions relating to beryllium hydrolysis. They determined the enthalpy and entropy of formation of the species Be2(OH)3+ and Be3(OH)3+. Subsequently, Mesmer and Baes determined the enthalpies for these two species from the temperature variation of the respective equilibrium constants. They also determined a value for the species Be5(OH) + (66). Ishiguro and Ohtaki measured the enthalpies of formation of Be2(OH)3+ and Be3(OH)3+ calorimetrically in solution in water and water/dioxan mixtures (99). The agreement between the values is satisfactory considering the fact that they were obtained with different chemical models and ionic media. 

Therefore, the physical meaning of the solubility curve of a surfactant is different from that of ordinary substances. Above the critical micelle concentration the thermodynamic functions, for example, the partial molar free energy, the activity, the enthalpy, remain more or less constant. For that reason, micelle formation can be considered as the formation of a new phase. Therefore, the Krafft Point depends on a complicated three phase equilibrium. 

Here, AH(A-B) is the partial molar net adsorption enthalpy associated with the transformation of 1 mol of the pure metal A in its standard state into the state of zero coverage on the surface of the electrode material B, ASVjbr is the difference in the vibrational entropies in the above states, n is the number of electrons involved in the electrode process, F the Faraday constant, and Am the surface of 1 mol of A as a mono layer on the electrode metal B [70]. For the calculation of the thermodynamic functions in (12), a number of models were used in [70] and calculations were performed for Ni-, Cu-, Pd-, Ag-, Pt-, and Au-electrodes and the micro components Hg, Tl, Pb, Bi, and Po, confirming the decisive influence of the choice of the electrode material on the deposition potential. For Pd and Pt, particularly large, positive values of E5o% were calculated, larger than the standard electrode potentials tabulated for these elements. This makes these electrode materials the prime choice for practical applications. An application of the same model to the superheavy elements still needs to be done, but one can anticipate that the preference for Pd and Pt will persist. The latter are metals in which, due to the formation of the metallic bond, almost or completely filled d orbitals are broken up, such that these metals tend in an extreme way towards the formation of intermetallic compounds with sp-metals. The perspective is to make use of the Pd or Pt in form of a tape on which the tracer activities are electrodeposited and the deposition zone is subsequently stepped between pairs of Si detectors for a-spectroscopy and SF measurements. 

Numerous organic species are known to lead to the crystallization of the MFI-type structure (7). but the tetrapropylammonium cations can be considered to be the most specific. To our knowledge no thermodynamic data such as standard formation enthalpies (AfH°) and stabilization energies attributed to the organic species have been published to corroborate this experimental observation. The published thermodynamic data (AfG°, AfH°, AfS°. Cp) are for natural zeolites (8-11) or for organic-free synthetic zeolites. However. some data have been obtained by calculations using lattice energy minimization and extended Hiickel theory (1 2) or by semi-empirical methods based on addition of the thermodynamic functions of the oxide compo-... 

Bondi and Simkin presented a similar calculation for liquids, using the heat of vaporization (AHv) (241, 242). The purpose was to obtain an estimate of but in the process a value of the H bond increment, 5(OH) is derived. This increment is .. . a measure of (but not identical with) the heat of formation of the H bond,. . Values for 5(OH) are very similar to enthalpy values, though they are not intended as thermodynamic functions. Bondi gives an extensive discussion of their use with simple and polyhydric alcohols and a few other compound classes. Table 7-V compares 6(OH) and AH values. 

A 2nd and 3rd law analysis is given in the following table. We adopt AjH (Hf, g, 298.15 K) - 147.8 1.5 kcal mol". This result is based on the reasonable consistency of the two vapor pressure studies (2, 4) with each other and with our adopted thermodynamic functions as evidenced by the small values of the drift. Hultgren (8), using different thermodynamic functions and data available through 1966, recommended an enthalpy of formation of 148.0 1.0 kcal mol" based heavily on the study by Kibler et al. (4). Other values for AjH (291 (10) and Lowrie (11). 

A second and third law evaluation of seven studies yields an adopted enthalpy of formation value, AjH°(298.15 K, Zr, g) = 145.8 2.0 kcal mol". This adopted value is a weighted average of four vapor pressure studies (2, 5, 6, 7). Hultgren (8), using different thermodynamic functions and data available through 1967, recommended a enthalpy of foramtion (at 298.15 K) of 145.5 t 1.0 kcal mol", based primarily on the data of Skinner et al. (2). 

Johnson, G. K., Papatheodorou, G. N., and Johnson, C. E., 1980, The enthalpies of formation and high temperature thermodynamic functions of the arsenic sulfides AS4S4) and (AS2S3) Journal of Chemical Thermodynamics, v. 12, p. 545-57. 

The saturated vapour pressure of a-CdSe was measured in the temperature range 1016 to 1170 K using a gas flow method. Values for the entropy and the enthalpy of formation of a-CdSe at 298.15 were derived using the second law and an estimated heat capacity of a-CdSe. The experimental results were therefore re-evaluated by the review using both the second and the third law, the selected thermodynamic functions of selenium, the data for Cd in [89COX/WAG], the selected heat capacity of a-CdSe, and the selected entropy of a-CdSe in the case of the third law. The vaporisation was assumed to occur according to the reaction a-CdSe Cd(g) + The results were... 

The enthalpy of formation of a-ZnSe was also measured direcly in a quantitative DTA calorimeter by the reaction of the powdered elements. The value obtained at 707 K was recalculated by the review to 298.15 K using the selected thermodynamic functions of selenium, the heat capacity of Zn in [89COX/WAG], and the heat capacity expression of a-ZnSe in Section V.9.1.1.1 because a different set of auxiliary data was employed for the calculations in the paper. The value obtained was Af//° (ZnSe, ct,... 

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