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1.
The vaporization enthalpies and vapor pressures of acetoin, ethyl 3-hydroxybutyrate and ethyl 3-hydroxyhexanoate, found in a variety of foods and flavors, are evaluated at T = 298.15 K using correlation-gas chromatography; values of (48.7 ± 0.4), (55.9 ± 0.6) and (61.9 ± 0.6) kJ mol−1, respectively, were obtained. These values are in good agreement with estimated values. Vapor pressures of the standards as a function of temperature were also used to calculate vapor pressures of the target compounds and all resulting data were fit to second order polynomials. These polynomials were then used to predict boiling temperatures of both standards and target substances. Agreement with experimental boiling temperatures was generally within 10 K suggesting that vapor pressures are accurate to within a factor of two. Acetoin exists as an equilibrium mixture of monomer and dimer. This report provides an example of the utility of using correlation-gas chromatography to obtain thermochemical data on an impure material.  相似文献   

2.
The (p, ρ, T) properties of pure methanol, the (p, ρ, T) properties and apparent molar volumes V? of ZnBr2 in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T, m) values were described by an equation of state. For the solutions the experiments were carried out at molalities m = (0.05772, 0.37852, 0.71585 and 1.95061) mol · kg−1 of zinc bromide.  相似文献   

3.
Experimental data on density, viscosity, and refractive index at T = (298.15, 303.15, and 308.15) K, while speed of sound values at T = 298.15 K are presented for the binary mixtures of (methylcyclohexane + benzene), methylbenzene (toluene), 1,4-dimethylbenzene (p-xylene), 1,3,5-trimethylbenzene (mesitylene), and methoxybenzene (anisole). From these data of density, viscosity, and refractive index, the excess molar volume, the deviations in viscosity, molar refraction, speed of sound, and isentropic compressibility have been calculated. The computed values have been fitted to Redlich-Kister polynomial equation to derive the coefficients and estimate the standard errors. Variations in the calculated excess quantities for these mixtures have been studied in terms of molecular interactions between the component liquids and the effects of methyl and methoxy group substitution on benzene ring.  相似文献   

4.
The present study reports a DSC study of the sulfur heterocyclic compounds: 2,2’-bithiophene [492-97-7]; 2,5-thiophenedicarboxylic acid [4282-31-9]; 3-acetylthiophene [1468-83-3]; 2-thiopheneacetic acid [1918-77-0]; 3-thiopheneacetic acid [6964-21-2]; 1,4-dithiane sulfone [139408-38-1]; 1,3-oxathiane-3,3-dioxide (1,3-oxathiane sulfone) [109577-03-9] and 1,4-oxathiane-4,4-dioxide (1,4-oxathiane sulfone) [107-61-9] in the temperature interval T = 268 K and the melting temperatures. Temperatures, enthalpies and entropies of fusion are reported. 1,4-Oxathiane sulfone presents solid-solid phase transitions near to fusion. No additional solid-solid phase transitions were observed for the other solid compounds. For the compounds that are solids over the temperature interval, the heat capacity of the condensed phase was measured. Heat capacities at T = 298.15 K for the liquids 2-acetylthiophene [88-15-3]; methyl, 2-thiopheneacetate [19432-68-9]; methyl, 3-thiopheneacetate [58414-52-1] and thiazole [288-47-1] were also measured. The Cp,m (298.15 K) values obtained in this work were compared with the available experimental data and with values estimated with group contribution schemes.  相似文献   

5.
Heat capacity and enthalpy increments of ternary bismuth tantalum oxides Bi4Ta2O11, Bi7Ta3O18 and Bi3TaO7 were measured by the relaxation time method (2-280 K), DSC (265-353 K) and drop calorimetry (622-1322 K). Temperature dependencies of the molar heat capacity in the form Cpm=445.8+0.005451T−7.489×106/T2 J K−1 mol−1, Cpm=699.0+0.05276T−9.956×106/T2 J K−1 mol−1 and Cpm=251.6+0.06705T−3.237×106/T2 J K−1 mol−1 for Bi3TaO7, Bi4Ta2O11 and for Bi7Ta3O18, respectively, were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S°m(298.15 K)=449.6±2.3 J K−1 mol−1 for Bi4Ta2O11, S°m(298.15 K)=743.0±3.8 J K−1 mol−1 for Bi7Ta3O18 and S°m(298.15 K)=304.3±1.6 J K−1 mol−1 for Bi3TaO7, were evaluated from the low-temperature heat capacity measurements.  相似文献   

6.
Density data for dilute aqueous solutions of methanol, ethanol, 1-propanol, and 2-propanol are presented together with partial molar volumes at infinite dilution calculated from the experimental data. The measurements were performed at from T = (298.15 up to 573.15) K and at pressure close to the saturated vapor pressure of water, at p = 30 MPa and at pressure between these limits. The data were obtained using a high-temperature high-pressure flow vibrating-tube densimeter.  相似文献   

7.
The vapor pressures of crystalline and liquid phases of methyl p-hydroxybenzoate and of methyl p-methoxybenzoate were measured over the temperature ranges (338.9 to 423.7) K and (292.0 to 355.7) K respectively, using a static method based on diaphragm capacitance gauges. The vapor pressures of the crystalline phase of the former compound were also measured in the temperature range (323.1 to 345.2) K using a Knudsen mass-loss effusion technique. The results enabled the determination of the standard molar enthalpies, entropies and Gibbs free energies of sublimation and of vaporization, at T = 298.15 K, as well as phase diagram representations of the (p, T) experimental data, including the triple point. The temperatures and molar enthalpies of fusion of both compounds were determined using differential scanning calorimetry and were compared with the results indirectly derived from the vapor pressure measurements. The standard (p° = 105 Pa) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, of the compounds studied were derived from their standard massic energies of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpies of formation, in the gaseous phase at T = 298.15 K, were calculated and compared with the values estimated by employing quantum chemical computational calculations. A good agreement between experimental and theoretical results is observed. To analyze the thermodynamic stability of the two compounds studied, the standard Gibbs free energies of formation in crystalline and gaseous phases were undertaken. The standard molar enthalpies of formation of the title compounds were also estimated from two different computational approaches using density functional theory-based B3LYP and the multilevel G3 methodologies.  相似文献   

8.
(Liquid + liquid) equilibrium (LLE) data for the ternary system of (water + butyric acid + oleyl alcohol) at T = (298.15, 308.15, and 318.15) K are reported. Complete phase diagrams were obtained by determining solubility and the tie-line data. The reliability of the experimental tie lines was confirmed by using Othmer-Tobias correlation. The UNIFAC method was used to predict the phase equilibrium data. The phase diagrams for the ternary mixtures including both the experimental and correlated tie lines are presented. Distribution coefficients and separation factors were evaluated for the immiscibility region. A comparison of the solvent extracting capability was made with respect to distribution coefficients, separation factors, and solvent-free selectivity bases for T = (298.15, 308.15, and 318.15) K. It is concluded that oleyl alcohol may serve as an adequate solvent to extract butyric acid from its dilute aqueous solutions.  相似文献   

9.
The (p,ρ,T) and (ps,ρs,Ts) properties of {(1−x)CH3OH + xLiBr} over a wide range of state parameters are reported for the first time. The experiments were carried out in a constant volume piezometer over a temperature range from 298.15 K to 398.15 K, at 0.08421, 0.13617, 0.19692, 0.23133 and 0.26891 mole fractions and from atmospheric pressure up to 60 MPa. The experimental uncertainties are ΔT=±3 mK for temperature, Δp=±5·10−2 MPa for high pressure and Δp=±5·10−4 MPa for atmospheric pressure, Δρ=±3·10−2 kg · m−3 for density. An equation of state was derived for correlation of the experimental data of the solutions.  相似文献   

10.
Specific heat capacities (Cp) of polycrystalline samples of BaCeO3 and BaZrO3 have been measured from about 1.6 K up to room temperature by means of adiabatic calorimetry. We provide corrected experimental data for the heat capacity of BaCeO3 in the range T < 10 K and, for the first time, contribute experimental data below 53 K for BaZrO3. Applying Debye's T3-law for T → 0 K, thermodynamic functions as molar entropy and enthalpy are derived by integration. We obtain Cp = 114.8 (±1.0) J mol−1 K−1, S° = 145.8 (±0.7) J mol−1 K−1 for BaCeO3 and Cp = 107.0 (±1.0) J mol−1 K−1, S° = 125.5 (±0.6) J mol−1 K−1 for BaZrO3 at 298.15 K. These results are in overall agreement with previously reported studies but slightly deviating, in both cases. Evaluations of Cp(T) yield Debye temperatures and identify deviations from the simple Debye-theory due to extra vibrational modes as well as anharmonicity. The anharmonicity turns out to be more pronounced at elevated temperatures for BaCeO3. The characteristic Debye temperatures determined at T = 0 K are Θ0 = 365 (±6) K for BaCeO3 and Θ0 = 402 (±9) K for BaZrO3.  相似文献   

11.
The solubility of lithium bromide and lithium nitrate in solvents methanol, ethanol, 1-propanol, 2-propanol and 1-butanol were measured in the range between 298.15 and 338.15 K using an analytical gravimetric method. An empirical equation was used to fit the experimental solubilities and the Pitzer model with inclusion of Archer's ionic strength was used for the calculation of osmotic coefficients. The experimental data of system pressures (p) for the correlation of LiBr + ethanol, LiBr + 2-propanol at T (298.15-333.15 K) and LiNO3 + ethanol at T (298.15-323.15 K) were obtained from published literatures. Moreover, the parameters of the Pitzer model were re-correlated and were used to predict mean ion activity coefficients. A procedure was also presented to predict the solubility products of salts in pure organic solvent.  相似文献   

12.
The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y2Ti2O7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θD, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for CpCv. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H0=34.69 kJ mol−1 and S(T=298.15 K)−S0=211.2 J K−1 mol−1. The thermal conductivity shows a peak at ca. θD/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y2Ti2O7 is 2.8 W m−1 K−1, close to the calculated theoretical thermal conductivity, κmin, for fully coupled phonons at high temperatures.  相似文献   

13.
The phase equilibrium, at T = 298.15 and 313.15 K and several thermophysical properties (density, sound velocity, refractive index) at T = 283.15, 298.15 and 313.5 K of mixtures formed by a cyclic ether (tetrahydropyran, tetrahydrofuran) and 1-chloropropane has been studied. Excess Gibbs functions, excess volumes, excess isentropic compressibilities and refractive index deviations have been obtained from the experimental data. Both the molecular characteristics of the pure compounds and the molecular interactions in the mixing process have been used to analyse the results.  相似文献   

14.
The semirestricted non-primitive mean spherical approximation (npmsa) is used in combination with the PC-SAFT equation of state to model completely dissociating aqueous alkali halide systems. The salts are described using ion-specific parameters from tables and correlations. Upon analyzing aqueous electrolyte systems at infinite dilution of the salt it was concluded that for the arithmetic mean ion diameter of anion and cation, the semirestricted npmsa contribution gives no reliable results. Therefore, this parameter is adjusted in this work. The model was applied to aqueous alkali halide systems up to the solubility limit at T = 298.15 K. Mean ionic activity coefficients and osmotic coefficients were correlated with good results. The model was subsequently applied to temperatures up to T = 373.15 K and compared to liquid densities and to system pressures up to the solubility limit of the salts in water. The agreement between experimental data and the proposed equation of state is satisfactory for the liquid densities and excellent in case of the system pressures.  相似文献   

15.
16.
The heat capacity of LuPO4 was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K−1 mol−1, S0(298.15 K) = 99.74 ± 0.32 J K−1 mol−1, H0(298.15 K) − H0(0) = 16.43 ± 0.02 kJ mol−1, −[G0(298.15 K) − H0(0)]/T = 44.62 ± 0.33 J K−1 mol−1. The standard Gibbs free energy of formation of LuPO4 from elements ΔfG0(298.15 K) = −1835.4 ± 4.2 kJ mol−1 was calculated based on obtained and literature data.  相似文献   

17.
A commercial flow-mixing isothermal calorimeter was tested by measuring heat of mixing curves for exothermic, endothermic, S-shaped and double minimum molar excess enthalpy mixtures at high pressure. The results show this calorimeter is able to produce good quality data. Molar excess enthalpies for ethyl acetate mixed with a series of simple alkanols were measured at T = 298.15 K and p = 10 MPa.  相似文献   

18.
The ternary rare-earth zinc antimonides REZn1-xSb2 (RE=La, Ce, Pr, Nd, Sm, Gd, Tb) were prepared by heating at 1050 °C followed by annealing at 600 °C. For all members, single-crystal X-ray diffraction studies indicated that the Zn deficiency is essentially fixed, corresponding to the formula REZn0.6Sb2, with no appreciable homogeneity range. These compounds adopt the HfCuSi2-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). Single-crystal electrical resistivity measurements confirmed the occurrence of an abrupt resistivity decrease near 4 K for RE=Ce, and a less pronounced one for RE=La, Pr, and Gd. Except for the ferromagnetic Ce (Tc=2.5 K) and antiferromagnetic Tb (TN=10 K) members, all remaining compounds exhibit no long-range magnetic ordering down to 2 K, instead showing temperature-independent (RE=La), van Vleck (RE=Sm), or Curie-Weiss paramagnetism (RE=Pr, Nd, Gd).  相似文献   

19.
We report the synthesis, crystal structure determination, magnetic and low-temperature structural properties of a new cobalt antimony oxo-bromide. CoSb2O3Br2 crystallizes in the triclinic crystal system, space group P−1, with the following lattice parameters: a=5.306(3) Å, b=7.812(4) Å, c=8.0626(10) Å, α=88.54(3)°, β=82.17(3)°, γ=80.32(4)°, and Z=2. The crystal structure was solved from single crystal X-ray data and refined on F2, R1=3.08. The structure consists of layers made up by three building blocks, [CoO4Br2], [SbO3Br], and [SbO3] that are connected via edge- and corner-sharing so that structural Co-Co dimers are formed. The layers have no net charge and are only weakly connected by van der Waals forces to adjacent layers. Above ∼25 K the magnetic susceptibility is independent of the magnetic field and can be very well described by a Curie-Weiss law. Below 25 K the susceptibility passes through a maximum and decreases again that is typical for the onset of long-range antiferromagnetic correlations. Long-range antiferromagnetic ordering is observed below TN∼9 K indicating substantial inter-dimer exchange coupling between Co-Co dimers within the layers. However, according to the heat capacity results only a minute fraction of the entropy is associated with the long-range ordering transition. The phonon anomalies observed for T<6 K in Raman scattering and an anomaly in the specific heat point to a structural instability leading to a loss of inversion symmetry at lowest temperatures.  相似文献   

20.
A high pressure flow-mixing isothermal calorimeter is used to determine the excess molar enthalpies of methylformate + (1-propanol, 2-propanol, 1-butanol, 2-butanol and 1-pentanol) at T = 298.15 K and p = (5.0, 10.0) MPa, and methylformate + 1-propanol at T = 333.15 K and p = 10.0 MPa. The Redlich-Kister equation is fit to the experimental results.  相似文献   

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