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Dissociation pressure and standard dissociation enthalpy of RuO2
No full textThe absolute dissociation oxygen pressure p above RuO2 was measured by the torsion-effusion method. By a least-square treatment of the data, the following equation for the temperature dependence of these pressures in the temperature (T) range 986-1221 K was selected: log(p) = (10.52 +/- 0.30) - (15,143 +/- 400)/ T, where p is measured in kPa. By treating the data by the second- and third-law methods the standard enthalpy associated with the dissociation of RuO2 (310 +/- 4 kJ mol(-1)) was derived. A comparison with literature data is also reported. (C) 2003 Elsevier B.V. All rights reserved
Vapor Pressures of Gallium Trifluoride, Trichloride, and Triiodide and Their Standard Sublimation Enthalpies
No full textThe vapor pressures of gallium trihalides GaF(3), GaCl(3), and Gal(3) were measured by a torsion effusion apparatus, and their temperature dependences fit the following equation: log(p/Pa) = (14.30 +/- 0.30) - (12600 +/- 200)/(T/K) (from 808 to 958 K), log(p/Pa) = 13.80 - 3800/(T/K) (from 289 to 308 K), and log(p/Pa) = (14.00 +/- 0.50) - (5130 +/- 150)/(T/K) (from 345 to 401 K) for GaF(3), GaCl(3), and Gal(3), respectively. Both GaF(3) and Gal(3) vaporize practically congruently in monomeric Form while GaCl(3) is in dimer form. Treating the vapor pressures by second- and third-law methods, the selected standard enthalpies Delta H degrees(298 K) = (252 +/- 4) kJ.mol(-1), (89 +/- 2) kJ.mol(-1), and (100.5 +/- 2.0) kJ.mol(-1) associated with the Sublimation of GaF(3), GaCl(3), and Gal(3), respectively, were obtained
Torsion measurement of orpiment vapor pressure
No full textTotal vapor pressures of orpiment, As2S3, were measured by the torsion effusion method, and their dependence was found to fit the following equation: log(p/kPa) = (14.14 +/- 0.20) - (9160 +/- 200)center dot(T/K) in the temperature range (501 to 583) K. The vapor molecular weight, evaluated at some temperatures in the covered range using the Knudsen equation on the vapor pressure measurements, was found to be equal to 250 +/- 20 g center dot mol(-1), which confirmed that, as reported in the literature, the primary sublimation processes of orpiment are As2S3(s) = As2S3(g) and As2S3(s) = (1/2)As4S4(g) + (1/2)S-2(g). Increasing the temperature does not change the importance of both reactions so that the second-law enthalpies associated with both reactions are comparable and equal to Delta H degrees(542 K) = 175 +/- 4 kJ center dot mol(-1)
Torsion vapor pressures and sublimation enthalpies of arsenic triselenide and tritelluride
No full textTotal vapor pressures of As2Se3 and As2Te3 were measured by the torsion-effusion method, and their temperature dependences were found to fit the following equations: As2Se3(s), log(p/kPa) = (12.20 +/- 0.20) to (9170 +/- 130)/(T/K) and As2Te3(s), log(p/kPa) = (10.45 +/- 0.20) to (8185 +/- 150)/(T/K). Considering the complex mode of vaporizing of As2Se3, the mean second-law enthalpy and entropy values associated to the sublimation of 1 mol of the vapor mixture at the mid-point temperature, Delta H degrees(587 K) = (175 +/- 3) kJ center dot mol(-1) and Delta S degrees(587 K) = (233 +/- 4) J center dot K-1 center dot mol(-1), were calculated from the temperature dependence of its vapor pressure. As2Te3 dissociates upon sublimation yielding As-4(g) and Te(s). Both As-4(g) and Te-2(g) are present in the vapor over Te-saturated As2Te3, where the Te-2(g) partial pressures are considered equal to the vapor pressure of the pure element. On this basis, treating the pressure data by second- and third-law methods, the standard sublimation enthalpy associated to the sublimation reaction, As2Te3(s) = 0.5 As-4(g) + 3 Te(s), Delta H degrees(298 K) = 81 +/- 2 kJ center dot mol(-1), was determined
Torsion Vapor Pressures and Sublimation Enthalpies of Aluminum Trifluoride and Aluminum Trichloride
No full textThe vapor pressures of solid AlF(3) and AlCl(3) were measured by the torsion-effusion method. Their temperature dependences fit the following equations: log(p/kPa) = (11.70 +/- 0.20) - (14 950 +/- 200)(T/K) (from (956 to 1113) K) and log(p/kPa) = (15.50 +/- 0.30) - (6200 +/- 200)(T/K) (from (321 to 378) K) for AlF(3) and AlCl(3), respectively. Treating the measured vapor pressures by the second- and third-law methods, the average standard enthalpies of the sublimation of 1 mol solid AlF(3) and AlCl(3) to AlF(3)(g) and Al(2)Cl(6)(g), Delta(sub)H degrees (298.15 K) = (301 +/- 4) kJ.mol(-1) and (59 +/- 2) kJ.mol(-1), respectively, were calculated
Vapor Pressures and Sublimation Enthalpies of Copper Difluoride and Silver(I, II) Fluorides by the Torsion-Effusion Method
No full textVapor Pressures of Aluminum Tribromide and Aluminum Triiodide and Their Standard Sublimation Enthalpies
No full textTotal vapor pressures of AlBr(3) and AlI(3) were measured by a torsion effusion apparatus. Their temperature dependences are expressed by the equations log(p/Pa) = (14.78 +/- 0.60) - (4700 +/- 200)/(T/K) from (301.0 to 351.0) K and log(p/Pa) = (15.52 +/- 0.30) - (5960 +/- 150)/(T/K) from (359.5 to 419.5) K for AlBr(3) and AlI(3), respectively. Practically, AlBr(3) vaporizes in a dimeric form, while AlI(3) vaporizes in monomeric and dimeric forms. Treating the vapor pressures of AlBr(3) by second- and third-law methods, the standard sublimation enthalpy Delta H degrees(298 K) = (90 +/- 4) kJ.mol(-1) was derived. For AlI(3), treating the partial pressures of monomer and dimer gaseous species, deduced from the measured total vapor pressures and the constant of dimer-monomer equilibrium reported in the literature, by second- and third-law methods, the standard enthalpies Delta H degrees(298 K) = (110 +/- 4) kJ.mol(-1) and Delta H degrees (298 K) = (119 +/- 4) kJ.mol(-1) associated to the sublimation reactions of AlI(3) according to the AlI(3)(s) -> AlI(3)(g) and 2AlI(3)(s) -> Al(2)I(6)(g), respectively, were selected
A Study on the Sublimation of Gallium Tribromide
No full textThe temperature dependence of the total vapor pressure of GaBr(3) measured by the torsion-effusion method over the temperature range (300 to 357) K is represented by the following equation: log(p/Pa) = (16.1 +/- 0.6) - (5250 +/- 200)(K/T). This compound Sublimes to the monomer and dimer species. From the temperature dependence of the dissociation, and the equilibrium constant of the dimer found in the literature, the partial pressures of both forms were evaluated from which the second- and third-law standard enthalpies of the sublimation reactions, GaBr(3)(s) = GaBr(3)(g) and GaBr(3)(s) = 1/2Ga(2)Br(6)(g), were calculated: Delta(sub)H degrees(298 K) = (92.5 +/- 2.0) kJ.mol(-1) and (50.5 +/- 2.0) kJ.mol(-1) for the monomer and dimer forms, respectively
Vapor Pressure of Zirconium Tetrafluoride
No full textMeasurements were made of the vapor pressures of zirconium tetrafluoride by using a torsion effusion apparatus. The temperature dependence fit the equation: log(p/Pa) = (15.20 +/- 0.15) - (11 900 +/- 200)/(T/K) (from 685 to 828 K). The compound vaporizes congruently in the monomeric form. With treatment of the measured vapor pressures by second- and third-law methods, the standard sublimation enthalpy Delta H-sub degrees(298 K) = (239 2) kJ . mol(-1) was obtained
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