Showing papers on "Standard molar entropy published in 1998"
TL;DR: In this article, Gschneider et al. calculated the heat capacity of rare earth hydroxides from low-temperature heat capacity measurements and derived the entropy and enthalpy of formation.
75 citations
TL;DR: In this paper, the molar heat capacity of borazane BH 3NH 3 was determined in the 10-289 K range using two different adiabatic calorimeter systems.
55 citations
TL;DR: In this paper, the heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range.
Abstract: The heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range. Near the upper temperature limit of our data, the heat capacity observed by DSC agrees with that reported by Geisinger et al. (1987) based on a vibrational model of their infrared and Raman spectroscopic data. However, with decreasing temperature, the Cp observed by DSC is progressively higher than that predicted from the vibrational model, suggesting that the standard entropy of K2Si4O9 is likely to be larger than 198.9 ± 4.0 J/K · mol computed from the spectroscopic data. A fit to the DSC data gave: Cp(T) = 499.13 (±1.87) − 4.35014 · 103(±3.489 · 101) · T
−0.5, with T in K and average absolute percent deviation of 0.37%. The room-temperature compressibilities of kalsilite and leucite, hitherto unknown, have been measured as well. The data, fitted to the Murnaghan equation of state, gave K
o = 58.6 GPa, K
o
′ = 0.1 for kalsilite and K
o = 45 GPa, K
o
′ = 5.7 for α-leucite. Apart from the above mentioned data on the properties of the individual phases, we have also obtained reaction-reversals on four equilibria in the system K2O-Al2O3-SiO2. The Bayesian method has been used simultaneously to process the properties of 13 phases and 15 reactions between them to derive an internally consistent thermodynamic dataset for the K2O-Al2O3-SiO2 ternary. The enthalpy of formation of K2Si4O9 wadeite is in perfect agreement with its revised calorimetric value, the standard entropy is 232.1 ± 10.4 J/K · mol, ∼15% higher than that implied by vibrational modeling. The phase diagram, generated from our internally consistent thermodynamic dataset, shows that for all probable P-T trajectories in the subduction regime, the stable pressure-induced decomposition of K-feldspar will produce coesite + kalsilite rather than coesite + kyanite + K2Si4O9 (cf. Urakawa et al. 1994).
26 citations
TL;DR: In this article, the temperature, molar enthalpy, and molar entropy of triphenylethene were determined to be (340.95±0.02) kJ·mol−1, (20.6± 0.1) J·K−1·m−1.
24 citations
TL;DR: In this paper, a thermodynamic investigation of the conversion of chorismate2-(aq) to pyruvate(aq) + 4-hydroxybenzoate-(aq)} has been performed by using microcalorimetry and high-performance liquid chromatography.
Abstract: A thermodynamic investigation of the conversion of chorismate2-(aq) to {pyruvate-(aq) + 4-hydroxybenzoate-(aq)} has been performed by using microcalorimetry and high-performance liquid chromatography. The study used a genetically engineered sample of chorismate lyase that was prepared with the Escherichia coli ubiC gene. The calorimetric measurements led to a standard molar enthalpy change = −(144 ± 7) kJ mol-1 for this reaction at the temperature T = 298.15 K and ionic strength Im = 0. An estimated value of the standard molar entropy change = 222 J K-1 mol-1 for the above reaction was used together with the experimental value of to obtain a standard molar Gibbs free energy change ≈ −210 kJ mol-1 and an equilibrium constant K ≈ 1037 for the conversion of chorismate2-(aq) to {pyruvate-(aq) + 4-hydroxybenzoate-(aq)} at T = 298.15 K and Im = 0. Quantum mechanics (Gaussian 94 with a B3LYP functional and a 6-31G* basis set) was used to calculate values of absolute energies for the neutral and ionic species per...
21 citations
TL;DR: In this paper, thermogravimetric measurements of the equilibrium oxygen partial pressure (p(O 2 )) as a function of temperature and oxygen content have been made on GdBa 2 Cu 3 O y (Gd123) within the range 3×10 −4 atm≤ p (O 2 )≤ 1 atm and 450°C≤ T ≤ 800°C.
Abstract: Thermogravimetric measurements of the equilibrium oxygen partial pressure ( p (O 2 )) as a function of temperature and oxygen content have been made on GdBa 2 Cu 3 O y (Gd123) within the range 3×10 −4 atm≤ p (O 2 )≤1 atm and 450°C≤ T ≤800°C. The partial molar entropy Δ S (O 2 ) and enthalpy Δ H (O 2 ) of solution of oxygen in Gd123 are evaluated and discussed. The p (O 2 ) data on Gd123 are compared with measurements performed on NdBa 2 Cu 3 O y (Nd123) at 800°C and literature data for YBa 2 Cu 3 O y (Y123) at 600°C and 800°C. The orthorhombic/tetragonal transition temperature ( T O/T ) for Gd123 and Nd123 as a function of the oxygen partial pressure (1×10 −3 atm≤ p (O 2 )≤1 atm) has been determined by high temperature X-ray diffraction (HTXRD). The oxygen content values for the O/T transition ( y O/T ) at several p (O 2 ) values for Gd123 and Nd123 have been determined by means of thermogravimetric measurements. The obtained data in the y – T diagram supports the applicability of the quasichemical approximation in describing the O/T transition of Gd123 and Nd123 compounds. The effect of the R atom (R=Y, Gd, Nd) ionic size on the oxygen stoichiometry and phase stability of R123 compounds at high temperature is discussed, and a possible explanation is proposed which accounts for the lattice mismatch between Ba–O and CuO 2 layers.
21 citations
TL;DR: In this paper, the standard molar enthalpies of formation Δ f H m °(cr) at the temperature T =298.15 K were measured by using combustion calorimetry of 2-phenylphenol, 4-phenylon phenol, 2,6-diphenylphenolate, 2.2′-dihydroxybiphenolate, and 4,4′-diaphylophenolate.
13 citations
01 Jan 1998
TL;DR: In this article, some features of the states of aggregation in which matter is usually present in Nature, in particular, real gases, condensed phases, phase equilibria and solutions, are discussed.
Abstract: In this chapter we treat some features of the states of aggregation in which matter is usually present in Nature, in particular, real gases, condensed phases, phase equilibria and solutions.
13 citations
TL;DR: In this article, the standard molar enthalpy of combustion of crystalline 2,3,7,8-tetrachlorodibenzo-p-dioxin was determined by rotating-bomb calorimetry.
12 citations
TL;DR: In this paper, single phase CuGaSe2 films were prepared in a temperature range from 460°C to 560°C and had grain sizes between 0.5 and 5 µm, and the necessary values for the heat of formation H298 and the standard entropy S298 were estimated to be H298=-251 kJ/mol and S298=155 J/K mol.
Abstract: Polycrystalline CuGaSe2 thin films have been prepared onto glass by a chemical vapor deposition (CVD) method which uses iodine as the transport agent. The source material was a polycrystalline CuGaSe2 powder which was pressed into pellets. Single phase CuGaSe2 films were prepared in a temperature range from 460°C to 560°C and had grain sizes between 0.5 and 5 µm. Thermochemical calculations were performed for the system under equilibrium conditions to model the deposition process. The necessary values for the heat of formation H298 and the standard entropy S298 for CuGaSe2 were estimated to be H298=-251 kJ/mol and S298=155 J/K mol. The calculations are in good agreement with the experimental observations.
12 citations
TL;DR: In this paper, the authors measured the change in the chromatographic response ΔR of the oxaloacetate peak that accompanied the transaminase reaction and calculated the apparent equilibrium constants for several solutions under near equilibrium conditions.
TL;DR: In this article, the construction of an adiabatic calorimeter for the 15-300-k range is described, which is fully automated and set up in a helium refrigerator system.
TL;DR: In this article, the decomposition equilibria of ammonium samarium chlorides (NH₄)₂SmCl₅ and NH₆SmCl ₂O₃ were determined by total pressure measurements and derived their thermodymical data from decomposition functions.
Abstract: We determined the decomposition equilibria of ammonium samarium chlorides (NH₄)₂SmCl₅ and NH₄Sm₂Cl₇ by total pressure measurements and derived their thermody namical data from the decomposition functions. The enthalpies of formation were compared with the results of the solution calorimetry. The heats of solution of all solid phases in the system SmCl₃-NH₄Cl and of Sm₂O₃ were measured in 4n HCl. The enthalpies of formation of ammonium samarium chlorides were derived from the enthalpies of formation of SmCl₃ and of NH₄Cl and their heats of solution.Data by total pressure measurementΔH°B((NH₄)₂SmCl₅,f,₂₉₈) =-407,7 ± 2,9 kcal/mol;S0((NH₄)₂SmCl₅,f,₂₉₈) = 84,0 ± 4,5 cal/K-mol;ΔH°B((NH₄)Sm₂Cl₇,f,₂₉₈) = -576,8 ± 3,4 kcal/mol;S°(NH₄Sm₂Cl₇,f,₂₉₈) = 98,1 ± 5,5 cal/K-mol.Data by solution calorimetryΔH°B(SmCl₃,f,₂₉₈) = -248,1 ± 0,8 kcal/mol;ΔH°B((NH₄),SmCl₅,f,₂₉₈) = -404 ,3 ± 1,1 kcal/mol;ΔH°B(NH₄Sm₉Cl₇,f,₂₉₈)= -572,3 ± 1,8 kcal/mol.
TL;DR: In this article, the enthalpy of formation of gaseous OsO3 was computed to ΔH°B(OsO3,g,298) = -40,0 ± 3 kcal/mol.
Abstract: The heterogeneous reactions: OsO4,s =OsO4,g, 2OsO2,s = Oss + OsO4,g, Oss + 3OsO4,g = 4OsO3,g, OsO2,s + OsO4,g = 2OsO3,g and the homogeneous reaction OsO4,g = OsO3,g + 1/2 O2,g were determined by total pressure measurements. From this and from chemical transport reactions of OsO2 and Os with Osmium tetroxide, the enthalpy of formation of gaseous OsO3 was computed to ΔH°B(OsO3,g,298) = -40,0 ± 3 kcal/mol.
TL;DR: In this article, a linear correlation between enthalpy of formation from oxides and ionic radius of alkali-earth cations was used for the estimation of enthalpies of formation of CaCuO 2 and Ba 2 CuO 3.
TL;DR: In this article, a new Dubinin-Astakhov equation based on the extension of the potential theory of adsorption on microporous fractal solids and corresponding thermodynamic functions were formulated and applied for description of the experimental data of adoration on a carbon carbon.
Abstract: A new adsorption isotherm equation based on the extension of the potential theory of adsorption on microporous fractal solids and corresponding thermodynamic functions were formulated and applied for description of the experimental data of adsorption on a microporous carbon. The comparison of the obtained results with the original Dubinin-Astakhov equation is presented. In this paper the dependence of thermodynamic functions (the differential molar enthalpy of adsorption ΔH and the differential molar entropy of adsorption ΔS) on the fractal dimension D are discussed, as well.
TL;DR: In this article, anchovy fish meal with an approximate uniform moisture content of 10% was used for the measurement of the isosteric heat or differential enthalpy, as a function of moisture content, showed a maximum value around 4.5 g of water/100 g d. s.
Abstract: Anchovy fish meal with an approximate uniform moisture content of 10% was used for this study. Vapor adsorption isotherms were determined at 25 ° C, 35 ° C and 45 ° C. The differential and integral thermodynamic properties were estimated using the Othmer method. The isosteric heat or differential enthalpy, as a function of moisture content, showed a maximum value around 4.5 g of water/100 g d. s. The heat of sorption increased gradually with an increase in sorbed water until reaching its maximum value near the monolayer, and at a given moisture content, decreasing with temperature. The molar entropy values obtained were high at low water contents and fell to a minimum near the monolayer value.
TL;DR: In this paper, the heat capacity of ammonium hexabromoplatinate (NH4)2PtBr6 was measured from T=6 K to T=320 K by using adiabatic calorimetry.
Journal Article•
TL;DR: In this article, the results of square-wave voltammetry and spectroscopy were compared quantitatively for the vanadium-containing glass, and for the iron-doped glass, the comparison was only qualitative.
Abstract: Glass melts and glasses with the basic composition NaPO 3 .2Sr(PO 3 ) 2 doped with V 2 O 5 and Fe 2 O 3 were studied with the aid of square-wave voltammetry and spectroscopic methods. From the square-wave voltammetry in the glass melt, a linear dependence of the peak potentials on the temperature was obtained. The standard enthalpy ΔH 0 , the standard entropy ΔS 0 and log(C ox /C red ) of the transitions Fe 3+ /Fe 2+ and V 4+ /V 3+ were calculated. The diffusion coefficients calculated from the peak currents measured follow Arrhenius' law. By means of electron spin resonance, the concentration of V 4+ was determined. The corresponding extinction coefficients for the V 4+ bands were calculated from the absorption spectra. Concerning the vanadium-containing glass, the results of square-wave voltammetry and spectroscopy were compared quantitatively. For the iron-doped glass, the comparison was only qualitative.
TL;DR: In this paper, the potential dependence of the heat-monitoring signal and of the photocurrent has been measured at a CdSe electrode (polycrystalline film on Ti) in 0.1 mol l − 1 aqueous KOH under 600 nm illumination.
TL;DR: In this article, the dominant gaseous complexes YAl₃Br₁₂ and YAlII₆₈ were generated in the chemical trans-port reactions of YAl and YI with AlI.
Abstract: The dominant gaseous complexes YAl₃Br₁₂ and YAl₃I₁₂ were generated in the chemical transport reactions of YBr₃ with AlBr₃ and YI₃ with AlI₃. The enthalpy of formation ΔH⁰B(YAl₃Br₁₂,g,₂₉₈) = -484,5 ± 6 kcal/mol and the standard entropy S°(YA₁₃B₁₂,g,₂₉₈) = 290,0 ± 7,5 cal/K·mol have been calculated. It follows from total pressure measurements of mixtures of YBr₃,ₛ with AlBr₃,₁ and YI₃,ₛ with AlI₃,₁ respectively, that complexes YAl₃Br₁₂,ₛ and YAl₃I₁₂,ₛ do not exist up to the boiling points of the aluminium trihalides.
TL;DR: In this article, the standard molar enthalpies of formation of liquid and gaseous compounds were determined by oxygen bomb combustion calorimetry, and the vapor pressures were measured at different temperatures by a static method.
Journal Article•
TL;DR: In this paper, a phosphate glass melt with the basic composition of NaPO 3.2Sr(PO 3 ) 2 doped with various oxides of polyvalent elements was studied with the aid of square-wave voltammetry.
Abstract: A phosphate glass melt with the basic composition of NaPO 3 .2Sr(PO 3 ) 2 doped with various oxides of polyvalent elements (Fe 2 O 3 , As 2 O 3 , Sb 2 O 3 , CuO and SO 4 2- ) was studied with the aid of square-wave voltammetry. The standard potentials depended linearly on temperature. The standard enthalpy ΔH° and the standard entropy ΔS° of the attributed redox reactions were calculated from the standard potentials measured. The diffusion coefficients were determined from current densities obtained and fulfilled the Arrhenius' law. Both thermodynamics of the redox equilibria and diffusion coefficients are compared with those measured in soda-lime-silica glasses.
TL;DR: In this article, the potential dependence of the heat-monitoring signal and of the photocurrent has been measured at a CdSe electrode (polycrystalline film on Ti) in 0.1 mol l − 1 aqueous KOH under 600 nm illumination.
Abstract: Photocalorimetry in conjunction with thermodynamical analysis has been employed to characterize the photocorrosion reaction of a semiconductor electrode. The potential dependence of the heat-monitoring signal and of the photocurrent has been measured at a CdSe electrode (polycrystalline film on Ti) in 0.1 mol l − 1 aqueous KOH under 600 nm illumination. From these measurements a characteristic potential ( E *=−0.21±0.02 V versus SHE) is obtained which connects the reversible potential and the Peltier coefficient of the corrosion reaction. These quantities are specific for a given reaction. Values of E * have been calculated for thermodynamically possible corrosion reactions of CdSe from the respective standard potential, standard entropy change and heat of transport. Good agreement between the measured and calculated values of E * and the photocalorimetric detection of a light-absorbing corrosion film indicate that CdSe+2OH − →Cd(OH) 2 +Se+2e − is the predominating corrosion reaction under the present conditions.
TL;DR: In this article, the molar heat capacity of borazane BH 3NH 3 was determined in the 10-289 K range using two different adiabatic calorimeter systems.
Abstract: The molar heat capacity of borazane BH 3 –NH 3 was determined in the 10–289 K range. Two different adiabatic calorimeter systems, each using the classical heat-step method, were applied for the measurements. The molar standard entropy of borazane at T =298.15 K was determined to be S 0 =96.34 J K −1 mol −1 . For the phase transition at T =224 K, a transition entropy of Δ S =6.87 J K −1 mol −1 was calculated from the heat capacity data. The results of X-ray powder diffraction confirm an order–disorder transition with a change of the lattice structure from orthorhombic to tetragonal. From low-temperature differential scanning calorimetry, a transition enthalpy of Δ H =1.34 kJ mol −1 was found, the transition enthalpy derived from the heat capacity is Δ H =1.48 kJ mol −1
01 Jan 1998
TL;DR: In this article, a linear correlation between enthalpy of formation from oxides and ionic radius of alkali-earth cations was used for the estimation of enthalpies of formation of CaCuO2 and Ba2CuO3.
Abstract: Optimized experimental data and estimated values are utilized for the assessment of thermochemical functions of alkaliearth cuprates. For the determination of temperature dependences of heat capacities the Neumann‐Kopp additive rule was employed. Values of standard enthalpy of formation and molar entropy of Ca2CuO3, SrCuO2 ,S r 2CuO3 and BaCuO2 were optimized from experimental results. For the estimation of enthalpies of formation of CaCuO2 and Ba2CuO3 a linear correlation between enthalpy of formation from oxides and ionic radius of alkali-earth cations was used. Molar entropy of CaCuO2 and Ba2CuO3 was estimated using the modified contribution method. # 1998 Elsevier Science B.V.