Sublimation enthalpies listed

The highlight of the chapter is the presentation in an analytical form of the temperature dependences of the reduced Gibbs free energy for 105 individual compounds, supplemented by the listing of their formation enthalpy under standard conditions AfH°(0), as well as of the atomization enthalpies AatH°(0) for the gaseous compoimds and the sublimation enthalpies AsubW°(0) for solid-state samples. These extensive data represent complete and consistent sets and may therefore be incorporated into relevant databases or individual programs for routine calculations of the thermodynamic parameters for equilibria involving the participation of rare-earth fluorides or chlorides. 

The heats of formation of chemical elements in standard state are taken as zero. The list of such elements is known, for example, [13] and mainly incorporates elements in solid state. Thus the single-atom gas formation enthalpy in these cases equals the sublimation enthalpy and is determined by physical and chemical criteria of the process. The sublimation comes to diffusion movements of heated particles into the surface layer with further effusion (outflow). The diffusion activation energies in external and internal regions are quite different... 

The printed data output step 4 lists the values for the constants A and B of the general vapor pressure equation and the enthalpy and entropy of vaporization or sublimation. 

The vapor pressures of ZrF (cr) in the temperature range 617-1150 K were determined by many investigators using various methods. Based on the reported vapor pressure data, the corresponding heats of sublimation are evaluated by the 2nd and 3rd law methods. Using the 3rd law Ag j H(298.15 K) and AjH"(ZrF, cr, 298.15 K) = -456.8 kcal mol", the enthalpies of formation at 298.15 K for ZrF (g) are evaluated. The results are presented in the table below. The values of AjH"(ZrF, g, 298.15 K), listed in the last column of this table are in excellent agreement which indicate that the estimated missing vibrational frequencies and... 

Ikeda et al. [343] made extensive measurements on the sublimation of different molybdenum oxides and determined the partial pressures of the species listed in Table 12. The dissociation enthalpies obtained are based on a second-and third-law evaluation and agree fairly well with those given in the review by Gingerich [21]. 

As evident from an analysis of thermodynamic data (primarily of the enthalpies of formation and sublimation) listed for several hundreds of substances in a reference book [4], determination of these constants by the third-law method yields values more precise, on the average, by an order of magnitude than those obtained using the second-law method. This can be traced to A, H depending differently on random and systematic errors in determination of the true reactant temperature and measurement of the variables P, J, or k, a point which becomes obvious when comparing Eqs. 4.10-4.12 with Eq. 4.18 below... 

Hougen et discuss the estimation of thermodynamic properties from molecular structure data. Gambill, in numerous articles to be found in the four volumes listed, deals with methods for the prediction of heat capacities of liquids and gases, enthalpies of vaporization, fusion and sublimation, critical temperature and pressure, and p, K, T data, including liquid densities. Dasent < presents methods for the estimation of the standard Gibbs energy of formation of non-existent compounds and compounds of low stability by procedures based on the use of ionic and covalent models. 

The standard enthalpies of sublimation of rare-earth metals have been measured by a number of workers. Hultgren et al. (1973) have discussed the sources of data and error estimates in their tabulation. Later Morss (1976) has also briefly discussed these data in his comprehensive discussion on thermochemical properties of the lanthanides. Recently Bratsch and Lagowski (1985) have listed a set of values of the sublimitation enthalpies which are also listed in table 1. The values of AH°f for rare-earth metals recommended in table 1 have been used in the recalculation of D values. 

Full sets of recommended data for standard temperature 298.15 K are listed in Table 43. The recommended enthalpies of sublimation were used to calculate the enthalpies of formation Afff (RCl3, g 298). The enthalpies of formation of crystalline RCI3 necessary for such calculations were taken from Table 27 (fifth column). 

In addition, the above A H° 298) values and the enthalpies of atomization AatH°(RCl3, 298) recommended by Chervonnyi and Chervonnaya (2007g) allowed us to calculate the same parameter for gaseous dimers of the lanthanide trichlorides. Selected values of the enthalpy of sublimation, the enthalpy of formation, and enthalpy of atomization are listed in Table 51. All calculations were performed by taking the needed parameters from IVTANTERMO (2004). 

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