Entropy of sublimation

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

Linear least squares treatments of plots of the logarithm of the vapor pressure versus the reciprocal temperature were performed. The second-law enthalpy and entropy of sublimation at the median temperature are proportioned to the slope and... 

Heats and entropies of sublimation and formation of Pu-intermetallics at median temperature and 298 K. 

A.G. Turnbull, Thermochemistry of Biscyclopentadienyl Metal Compounds. II. Entropy of Sublimation, Australian Journal of Chemical, Vol.20, 1967, pp.2757-2760. 

From trends in the enthalpies and entropies of sublimation for the other alkali sulfates (4), we would estimate a H (1200 K)... 

Table V-23 Experimental values of the enthalpy and entropy of sublimation of Se02(cr) from vapour pressure measurements over the temperature intervals in column 2.

Table V-36 Determinations of the enthalpy and entropy of sublimation of a-SnSe.

The total pressure of the vapour in equilibrium with (3-SnSe was measured in the temperature range 862 to 920 K using the Knudsen effusion technique. The enthalpy and entropy of sublimation according to the reaction a-SnSe SnSe(g) were calculated by the review from the reported vapour pressure expression and the selected heat capacities of SnSe(g) and a-SnSe, the enthalpy of transformation a-SnSe —> (3-SnSe being 1.28 kJ-mof (cf V.7.4.1.2), and a heat capacity expression of (3-SnSe being identical to that of a-SnSe, yielding (SnSe, a, 298.15 K) = (188.2 + 20.0) kJ-mol and... 

The enthalpy of formation of a-WCl has been determined calorimetrically and the heat of sublimation of WBrj measured. The enthalpy of formation of WBrj(g)at 298 K has been calculated as 201.67 kJmol . Reduction of WF on a tungsten wire in vacuo at 873 K allowed WFj, WjFj, WjFjj, and W Fjq to be detected by mass spectroscopy and the heat and entropy of sublimation of WF, and bond... 

The sublimation of ThBr4(cr) was studied in the temperature range 631 to 768 K by the torsion-effusion method. Supplementary mass-spectrometric measurements indicated that only monomeric ThBr4(g) exists in the vapour at these temperatures, in agreement with the molecular weight derived from the torsion-effusion measurements. The entropy of sublimation was considered to be more consistent with a distorted tetrahedral stmc-ture, but later theoretical studies indicate that the ThBr4(g) molecule, in fact has tetrahedral symmetry, as discussed in Section VIII.3.1.4.1. 

Anhydrous zirconium (IV) iodide is an orange crystalline solid which fumes heavily in air. It dissolves completely in water with the liberation of energy. According to Blumen-thal, it has a heat of formation of 90 kcal./mol at 25°. It sublimes at 431° at atmospheric pressure and melts at 499° at elevated pressures. Its heat and entropy of sublimation are 29.0 and 41.2 kcal./mol, respectively. Its magnetic susceptibility is —0.238 X 10 c.g.s. electromagnetic units. 

Binary Systems and Related Compounds.—Halides. The vapourization characteristics of ReBr3 have been studied by effusion techniques and the enthalpy and entropy of sublimation determined as 200 kJ mol and 227 e.u. (per mole of trimer), respectively.The X-ray characteristics of rhenium(iii) iodide, prepared from HRe04 and HI in MeOH at 80-90 °C, have been reported. 

Mass spectrometric measurements have been used to determine the vapour pressures of GaFa and (GaFg)2. Calculations of the enthalpies and entropies of sublimation gave the following results GaFg (298 K) 58.8 ... 

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