1,721,014 research outputs found
Bruno Brunetti e Roberto Derobertis Identità, Migrazioni e postcolonialismo in Italia
Full text linkBruno Brunetti e Roberto Derobertis Identità, Migrazioni e postcolonialismo in Italia
(Bari, Progedit, 2014, ISBN: 978-88-6194-223-3)
di Nicoletta Valloran
Vapor pressures, standard molar enthalpies, entropies Gibbs energies of sublimation and heat capacities of 2,5- and 3,5-dibromobenzoic acids
No full textThe vapor pressures of solid and liquid 2,5- and 3,5-dibromobenzoic acids were determined by torsion-effusion and thermogravimetry (under both isothermal and non-isothermal conditions), respectively. The molar enthalpies of sublimation Delta H-g(cr)m degrees(T-m) and vaporization Delta H-g(l)m degrees(T-m) were calculated, respectively, at the middle temperature (T-m) of the respective temperature intervals from the temperature dependence of vapor pressure derived by the experimental torsion-effusion and thermogravimetric data. The melting temperatures and the molar enthalpies of fusion of these compounds were determined by d.s.c. as well as the molar heat capacities (in the temperature range from 288.2 K to 326.2 K). The molar enthalpies and entropies of sublimation and vaporization obtained by torsion-effusion and thermogravimetry, respectively, were adjusted to the reference temperature of 298.15 K using the estimated heat capacity differences between gas and liquid for vaporization experiments and the estimated heat capacity differences between gas and solid for sublimation experiments. Therefore, the averages of the standard (p degrees = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15 K, have been derived: [GRAPHICS] (c) 2012 Elsevier B.V. All rights reserved
Thermochemical study of 2,4-, 2,6- and 3,4-dihydroxybenzoic acids in the liquid phase using a TG apparatus
No full textThe vapor pressures of the liquid 2,4-2,6-and 3,4-dihydroxybenzoic acids were determined by thermogravimetry(TG) under both isothermal and non-isothermal conditions, respectively. D.s.c. and isothermal measurements after a thermal treatment were used to verify that no appreciable decomposition process occurs in the three isomers investigated in the temperature range considered. From the temperature dependence of vapor pressure derived by the experimental data the molar enthalpies of vaporization Delta(g)(I)H(m)degrees()were determined, respectively, at the middle (7) of the respective temperature intervals. The melting temperatures and the molar enthalpies of fusion of these compounds were measured by d.s.c. The vapor pressures of these compounds in the solid state, measured by torsion-effusion technique, were compared with recently published data, while the corresponding molar sublimation enthalpies were determined. In order to validate the vapor pressure results determined by TG, the experimental vapor pressure data regarding solid ferrocene and 1,2-dihydroxybenzoic acid were successfully compared with literature values in the range 20-200 Pa. In addition, the experimental molar enthalpies of fusion were compared with those calculated by subtracting the molar vaporization enthalpies to the sublimation ones, both adjusted to their respective melting temperatures. Finally, the standard (p degrees = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, corrected at the reference temperature of 298.15K, have been calculated using the estimated heat capacity differences between gas and liquid for vaporization experiments and the estimated heat capacity differences between gas and solid for sublimation experiments. From the averages of the Delta(8)(cr)G(m)degrees(298.15 K) values the following increasing-order of volatility can be established for these three isomers, on the basis of the occurrence of infra-molecular and inter-molecular hydrogen bonds: 2,6-dihydroxybenzoic acid < 2,4-dihydroxybenzoic acid < 3,4-dihydroxybenzoic acid. (C) 2011 Elsevier B.V. All rights reserved
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
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 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)
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
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
Sublimation Enthalpies of some Methyl Derivatives of Uracil from Vapor Pressures Measurements
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
- …
