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Showing papers on "Standard molar entropy published in 1992"


Journal ArticleDOI
TL;DR: In this article, light scattering was used to determine the dependence of the critical micelle temperature on concentration for solutions of a polystyrene-block-poly(ethylene/propylene) copolymer in n-hexane, n-heptane and n-decane.
Abstract: Light scattering was used to determine the dependence of the critical micelle temperature on concentration for solutions of a polystyrene-block-poly(ethylene/propylene) copolymer in n-hexane, n-heptane, n-oxtane, n-decane, and n-dodecane. The results were used to estimated the standard Gibbs energy, ΔG°, the standard enthalpy, ΔH°, and the standard entropy, ΔS°, of micellation. The values of ΔH° were large and negative and were markedly dependent on the carbon number of the lower n-alkanes. The values of ΔG° are negative for all n-alkanes studied

37 citations


Journal ArticleDOI
TL;DR: In this article, the enthalpy of sublimation of ǫ-caprolactam was directly determined by a heat-conduction differential calorimeter: Δ sub H o m (338 K) = (86.30±0.22) kJ · mol −1.

32 citations


Book ChapterDOI
01 Jan 1992
TL;DR: In this article, the isobaric heat capacity (C p ) is used to calculate the variation with temperature of the entropy, the enthalpy, and the Gibbs free energy.
Abstract: Thermodynamic modeling of experimental or natural-phase equilibria has become an integral part of petrology. In this respect, the isobaric heat capacity (C p ) has manifold importance. First, C p data constitute the basis of third-law determinations of the entropy of minerals. Second, these data are needed to calculate the variation with temperature of the entropy, the enthalpy, and the Gibbs free energy. As a result, it necessary to know accurately heat capacities when retrieving thermodynamic information from phase equilibria data, especially when trying to separate the effects of the enthalpies and entropies of transformation.

19 citations


Journal ArticleDOI
TL;DR: In this article, the standard free energies of formation of zinc chalcogenides (ZnTe, ZnSe and α-ZnS) have been determined by an electrochemical technique using LiCl-KCl + 5 wt.% ZnCl 2 electrolyte.

18 citations


Journal ArticleDOI
01 Feb 1992
TL;DR: In this article, the authors compared the absorption properties of Pd95-xYxAg5 solid solution alloys with up to 6.3 at with those of binary alloys.
Abstract: Thermodynamic quantities for absorption of hydrogen by Pd95–xYxAg5 solid solution alloys with up to x = 6.3 at.% Y have been determined from measurements of pressure-composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 1000 Torr. The hydrogen absorption characteristics have been compared with those of the previously reported Pd–Ag and Pd–Y binary alloys. The relative partial molar enthalpy, ΔHH0, at infinite dilution of hydrogen in Pd95–xYxAg5 alloys increases in exothermicity with increasing Y content from that of Pd–5.0 at.% Ag, almost parallel to that in Pd–Y binary alloys. The relative partial molar entropy, ΔSH0, at infinite dilution in the ternary alloys decreases with Y content from that of Pd–5.0 at.% Ag alloy. The hydrogen solubility behavior at low hydrogen concentration in the Pd–Y–Ag alloys under a “constant volume” condition can be described as due to mainly the strong H–Y attractive pair interaction in the Pd host lattice. The stability of β-hydride and hydrogen concentration at αmax phase boundary increase following alloying with Y from that of Pd–5.0 at.% Ag alloy, respectively, and the changes in the properties with Y content are similar to that in Pd–Y binary alloys.

14 citations


Journal ArticleDOI
TL;DR: In this paper, the heat capacities of hexamethylbenzene-d 18 (HMB-d18 ) were measured at temperatures T between 4 K and 300 K, and the molar entropy of transition is 13.1 J·K −1 ·mol −1, which is 1.41 times as large as that of HMB-h 18.

14 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used x-ray diffraction to identify the equilibrium phases of a Galvanic cell with solid electrolytes and constructed a free energy vs.composition diagram for the system.
Abstract: Galvanic cells with solid electrolytes were used to determine activity‐composition diagrams in the systems. Activities of were determined from the measured electromotive force (EMF) values while those of were estimated by Gibbs‐Duhem integration. Equilibrium phases were identified by x‐ray diffraction. In the stability range of the rhombohedral phase , the activity of exhibited a drastic decrease with increasing amount of in all three systems. system showed the widest rhombohedral phase field and the lowest activity of (0.117) in the composition, , at 630°C. Partial molar entropies of dissolution of were determined from the temperature dependence of EMF. On the side, partial molar entropies of dissolution of were compared with a theoretical calculation of the configuration part of the partial molar entropy. A free energy vs.composition diagram was constructed for the system.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the viscosities of solutions of cholesterol in benzene, toluene, carbon tetrachloride, chloroform and 1,2-dichloroethane up to 0.4 mol kg −1 at 293, 298, 303, 313, 323 and 333 K have been measured.

13 citations


Journal ArticleDOI
TL;DR: In this article, the heat capacity of crystalline and liquid cyclohexanone oxime was measured by vacuum adiabatic calorimetry (T = 6 K to 300 K) and by the triple heat bridge method (t = 300 K to 450 K), and the melting temperature Tm = 362.5 K and molar enthalpy of fusion ΔfusHom = (12.7 ± 0.3 kJ·mol−1 were obtained by the latter method.

11 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of column tenperature on the capacity factor and selectivity of dipeptide isomers was investigated, and it was shown that the difference of their standard entropy change played more important role in the selectivity value than that of standard enthalpy change does.
Abstract: The effect of column tenperature on the capacity factor and selectivity of dipeptide isomers was investigated. It has been, observed that the variation in the logarithm of the capacity factor of dipeptide isomers is linearly dependent on the reciprocal of the absolute column temperature. The standard enthalpic change for dipeptide isomers is almost a constant, and the selectivity value is almost independent of the column temperature. It can be concluded that (1) the enthalpy change of dipeptide isomers in RP-HPLC is mainly determined by the molecular interaction in the mobile phase and (2) the difference of their standard entropy change play more important role in the selectivity value than that of standard enthalpy change does.

7 citations


Journal ArticleDOI
TL;DR: In this article, the excess molar Gibbs energy for (strontium + barium) oxides was determined in the temperature range 1430 K to 1530 K by means of mass spectrometry.

Journal ArticleDOI
TL;DR: In this article, the heat capacities of V3P and V3Si were measured in the temperature range from 150 to 350 K and the authors provided support for a value of 25.6±0.6 J/g
Abstract: The heat capacities of V3P and V3Si were measured in the temperature range from 150–350 K. At 298.15 K, we find Cp(V3P)=22.3±.2 J/g atom K and Cp(V3Si)=22.6±0.2 J/g atom K. At 150 K the heat capacity of V3P is 6% smaller than that of V3Si. Our data provide support for a value of 25.6 J/g atom for the standard entropy of V3Si at 298.15 K, and result in an estimated value of 23.5 J/g atom for the standard entropy of V3P at 298.15 K.

Journal ArticleDOI
TL;DR: In this paper, the influence of the molar mass and chemical composition of copolymers on the thermodynamics of the micellization process has been investigated using two polystyrene-block-poly(ethylene/propylene) copolymer with the same poly-styrene (PS) block length but different poly (ethylene) length (PEP).
Abstract: The influence of the molar mass and chemical composition of copolymers on the thermodynamics of the micellization process has been investigated using two polystyrene-block-poly(ethylene/propylene) copolymers with the same polystyrene (PS) block length but different poly(ethylene/propylene) lengths (PEP). Micelle formation was studied in n-octane and 5-methylhexan-2-one, selective solvents for PEP and PS blocks, respectively. Light-scattering measurements were carried out in order to determine the critical micelle temperature, Tcm, of the different micelle solutions. From Tcm and concentration data, the standard Gibbs energy, standard enthalpy and standard entropy of micellization were estimated. The characteristics of the copolymer and the block location in the micelle structure were found to influence the thermodynamics of the micellization process. Anomalous behaviour was observed for one copolymer in 5-methylhexan-2-one.

Journal ArticleDOI
TL;DR: In this article, the electrical conductivity of a perovskite-type compound, HoBa 2 Cu 3 O 6+x, was determined as a function of oxygen partial pressure (5 × 10 −1 ∼1 × 10 5 Pa) in the temperature range of 863∼1173 K by coulometric titration using a stabilized zirconia electrolyte.

Journal ArticleDOI
TL;DR: In this article, the free energy of formation of cadmium sulphide has been determined by an electrochemical technique using a molten salt electrolyte (LiCl-KCl+5 wt.% CdCl2) galvanic cell.

Journal ArticleDOI
TL;DR: In this article, the partial pressure of oxygen (PO2) in the tungsten-oxygen system has been measured by a thermogravimetric technique in the composition range of O/W=28975 between 1023 and 1223 K.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the absorption properties of Pd95-xYxAg5 solid solution alloys with up to 6.3 at with those of binary alloys.
Abstract: Thermodynamic quantities for absorption of hydrogen by Pd95–xYxAg5 solid solution alloys with up to x = 6.3 at.% Y have been determined from measurements of pressure-composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 1000 Torr. The hydrogen absorption characteristics have been compared with those of the previously reported Pd–Ag and Pd–Y binary alloys. The relative partial molar enthalpy, ΔHH0, at infinite dilution of hydrogen in Pd95–xYxAg5 alloys increases in exothermicity with increasing Y content from that of Pd–5.0 at.% Ag, almost parallel to that in Pd–Y binary alloys. The relative partial molar entropy, ΔSH0, at infinite dilution in the ternary alloys decreases with Y content from that of Pd–5.0 at.% Ag alloy. The hydrogen solubility behavior at low hydrogen concentration in the Pd–Y–Ag alloys under a “constant volume” condition can be described as due to mainly the strong H–Y attractive pair interaction in the Pd host lattice. The stability of β-hydride and hydrogen concentration at αmax phase boundary increase following alloying with Y from that of Pd–5.0 at.% Ag alloy, respectively, and the changes in the properties with Y content are similar to that in Pd–Y binary alloys.

Journal Article
TL;DR: In this article, the authors measured the retention volume, which characterizes the equilibrium partitioning of the solute vapor (alkane) between the mobile gas (helium) and stationary phases (aluminosilicate glass fibers).
Abstract: Gas chromatography is used as a useful and important tool for obtaining physicochemical information. Surface properties of aluminosilicate glass fiber have been studied by adsorption of vapors (alkanes C 5 -C 9 ) at a gas fiber interface. Unlike conventional adsorption techniques, gas chromatography allows the measurement of adsorption data down to very low vapor concentrations where the surface coverage approaches zero and only adsorbate (alkane)-glass fibers interactions are important. The zero coverage on Henry's law regions is considered. The fundamental parameter measured in gas chromatography is the retention volume, which characterizes the equilibrium partitioning of the solute vapor (alkane) between the mobile gas (helium) and stationary phases (aluminosilicate glass fibers). The standard free energy of adsorption (ΔG° A ), the differential heat of adsorption (ΔH A ) and the standard entropy of adsorption (ΔS° A ) are obtained from the retention volumen data

01 Jan 1992
TL;DR: In this paper, the activity ccefficients of silver nitrate in binary melts of AgNO, KNO, were determined by measuring a formation eel consisting of a silver and a nitrate electrode, in a temperature range of 513-583 K and in the concentration range allowed by the melting point of the mixture.
Abstract: 1991) Abstract-The activity ccefficients of silver nitrate in binary melts of AgNO,-KNO, were determined by ernfmeasurements in a formation eel1 consisting of a silver and a nitrate electrode, in a temperature. range of 513-583 K and in the concentration range allowed by the melting point of the mixture. Using a polynomial expression of the excess chemical potential, the excess Gibbs function and the characteristic constants of the investigated binary molten salt system were calculated. The excess molar entropy was calculated by combining the excess Gibbs function with calorimetric data on the excess enthalpy