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2.
Measurements leading to the calculation of the standard thermodynamic properties for gaseous dicyclohexylsulfide (Chemical Abstracts registry number [7133-46-2]) are reported. Experimental methods include adiabatic heat-capacity calorimetry, and inclined-piston gauge manometry combined with earlier reported measurements of combustion calorimetry, vibrating-tube densitometry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). Critical properties are estimated for dicyclohexylsulfide. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation are derived at selected temperatures between (298.15 and 520) K. 相似文献
3.
The heat capacity of water in the form of hexagonal ice was measured between T = 0.5 K and T = 38 K using a semi-adiabatic calorimetric method. Since heat capacity data below T = 2 K have never been measured for water, this study presents the lowest measured values of the specific heat of water to date. Fits of the data were used to generate thermodynamic functions of water at smoothed temperatures between 0.5 K and 38 K. Both our experimental heat capacities and calculated enthalpy increments agree well with previously published values and thus supplement other studies well. 相似文献
5.
Cryogenic heat capacities determined by equilibrium adiabatic calorimetry from T = (6 to 350) K on Li, Na, and K disilicates in both crystalline and vitreous phases are adjusted to end member composition and the vitreous/crystal difference ascertained. The thermophysical properties of these and related phases are estimated, compared, and updated. The values at T = 298.15 K of { S∘( T) − S∘(0)}/ R for stoichiometric compositions of alkali disilicate (M 2O · 2SiO 2): vitreous, crystal: Li, 16.30, 14.65; Na, 20.67, 19.47; and K, 23.26, 23.00. Entropy differences confirm greater disorder in the vitreous compounds compared with the crystalline compounds. The entropy data also show that disorder increases with decreasing atomic mass of the alkali ion. 相似文献
6.
The molar isobaric heat capacities of (methanol + 1-hexyl-3-methylimidazolium tetrafluoroborate) and (methanol + 1-methyl-3-octylimidazolium tetrafluoroborate) mixtures have been determined over the temperature range from 283.15 K to 323.15 K within the whole composition range. The excess molar heat capacities of investigated mixtures have been fitted to the Redlich–Kister equation at several selected temperatures. Positive deviations from the additivity of molar heat capacities have been observed in both examined systems. The results obtained have been discussed in terms of molecular interactions in binary mixtures. 相似文献
7.
The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an
automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample
container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements
on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the
inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase
transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively.
The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H (T)- H
298.15 K} and { S
(T)-S 298.15 K}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric
study was determined to be 99.9965% by fraction melting approach.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
The heat capacities of d-ribose and d-mannose have been studied over the temperature range from 1.9 to 440 K for the first time using a combination of Quantum Design Physical Property Measurement System and a differential scanning calorimeter. The purity, crystal phase and thermal stability of these two compounds have been characterized using HPLC, XRD and TG–DTA techniques, respectively. The heat capacities of d-Mannose have been found to be larger than those of d-ribose due to its larger molecular weight, and the solid–liquid transition due to the sample melting has also been detected in the heat capacity curve. The heat capacities of these two compounds have been fitted to a series of theoretical models and empirical equations in the entire experimental temperature region, and the corresponding thermodynamic functions have been derived based on the curve fitting in the temperature range from 0 to 440 K. Moreover, the phase transition enthalpy and melting temperature of these two compounds have also been determined from the heat flows obtained in DSC measurements. 相似文献
9.
Densities ( ρ) for binary systems of ( p-xylene or o-xylene + ethylene glycol dimethyl ether) were measured over the full mole fraction range at the temperatures of (298.15, 303.15 and 308.15) K along with the densities of the pure components. The excess molar volumes ( VE) calculated from the density data show that the deviations from ideal behaviour in the two binary systems are negative, and they become more negative with the temperature increasing. Surface tensions ( σ) of these binary systems were determined at the same temperatures (298.15, 303.15 and 308.15) K by the pendant drop method. The surface tension deviations ( δσ) for p-xylene system are negative over the whole composition range, and become less negative with the temperature increasing, but for the o-xylene system, δσ are negative at high o-xylene concentration, and change to positive with the o-xylene concentration decreasing. The VE and δσ were fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy ( Sσ) and surface enthalpy ( Hσ). 相似文献
10.
Experimental densities were determined in liquid phase for 1-heptanol and 2-heptanol at temperatures from 313 K to 363 K and pressures up to 22 MPa using a vibrating tube densimeter. Water and nitrogen were used as reference fluids for the calibration of the vibrating tube densimeter. The uncertainties of the experimental measurements in the whole range of reported data are estimated to be ±0.03 K for temperature, ±0.008 MPa for pressure, and ±0.20 kg · m ?3 for density. The experimental data are correlated using a short empirical equation of six parameters and the 11-parameter Benedict–Webb–Rubin–Starling equation of state (BWRS EoS) using a least square optimization. Statistical values to evaluate the different correlations are reported. Published density data of 1-heptanol are compared with values calculated with the 6-parameter equation using the parameters obtained in this work. The experimental data determined here are also compared with an available correlation for 1-heptanol. Densities of 2-heptanol at high pressure were not found in the literature and the data reported here represent the first set of data reported in the literature. Isothermal compressibilities and isobaric thermal expansivity are calculated using the 6-parameter equation for both alcohols within uncertainties estimated to be ±0.025 Gpa ?1 and ±4 × 10 ?7 K ?1, respectively. 相似文献
11.
The heat capacity of polycrystalline germanium disulfide α-GeS 2 has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K ?1 · mol ?1, 87.935 J · K ?1 · mol ?1 and 12.642 kJ · mol ?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol ?1, respectively. The thermodynamic functions of α-GeS 2 were calculated over the range (0 ? T/K ? 1250). 相似文献
13.
Heat capacity data and calculated thermodynamic functions are presented for DyNi 5, HoNi 5 and ErNi 5. λ-type thermal anomalies are noted at 12.0 K (DyNi 5), 4.1 K (HoNi 5) and 8.0 K (ErNi 5). Schottky-type anomalies are observed at higher temperatures. The λ and Schottky anomalies are ascribed to the destruction of ferromagnetic order and to crystal field excitation, respectively. A deficiency of magnetic entropy, compared to Rln(2 J + 1), is noted corresponding roughly to Rln2. This suggests that the ground state in the ordered materials is a doublet. ErNi 5 is analyzed using a Hamiltonian containing terms representing the crystal field and magnetic interactions. The analysis shows that a doublet ground state can result with reasonable values of the crystal field parameters. The parameters are shown to be consistent with the heat capacity behavior of ErNi 5. Ordering temperatures are not proportional to the de Gennes function. 相似文献
14.
The temperature dependencies of the molar heat capacities of ZnTeO 3, Zn 2Te 3O 8, CdTeO 3 and CdTe 2O 5 are determined. The experimental data are statistically processed using the least squares method to determine the parameters
in the equations for the corresponding compounds: Cp,m= a+ b( T/K)- c( T/K) -2. These equations and the standard molar entropies are used to determine Δ T0S0m, Δ TTH0m and (Φ 0m+Δ T,0H0m/ T) for T'=298.15 K. 相似文献
15.
The ( p, ρ, T) properties for n-butane in the compressed liquid phase were measured by means of a metal-bellows variable volumometer in the temperature range from 280 K to 380 K at pressures up to 200 MPa. The mole fraction purity of the n-butane used in the measurements was 0.9997. The expanded uncertainties ( k = 2) in temperature, pressure, and density measurements have been estimated to be less than ±3 mK; 1.4 kPa ( p ⩽ 7 MPa), 0.06% (7 MPa < p ⩽ 50 MPa), 0.1% (50 MPa < p ⩽ 150 MPa), and 0.2% ( p > 150 MPa); and 0.09%, respectively. In the region above100 MPa at T = 280 K and T = 440 K, the uncertainty in density measurements increases from 0.09% to 0.13% and 0.22%, respectively. Eight ( p, ρ, T) measurements at the same temperatures and pressures as the literature values have been conducted for comparisons. In addition, comparisons of the available equations of state with the present measurements are reported. 相似文献
16.
We determined apparent molar volumes V? at 298.15 ? ( T/K) ? 368.15 and apparent molar heat capacities Cp,? at 298.15 ? ( T/K) ? 393.15 for aqueous solutions of HIO 3 at molalities m from (0.015 to 1.0) mol · kg ?1, and of aqueous KIO 3 at molalities m from (0.01 to 0.2) mol · kg ?1 at p = 0.35 MPa. We also determined V? at the same p and at 298.15 ? ( T/K) ? 368.15 for aqueous solutions of KI at m from (0.015 to 7.5) mol · kg ?1. We determined Cp,? at the same p and at 298.15 ? ( T/K) ? 393.15 for aqueous solutions of KI at m from (0.015 to 5.5) mol · kg ?1, and for aqueous solutions of NaIO 3 at m from (0.02 to 0.15) mol · kg ?1. Values of V? were determined from densities measured with a vibrating-tube densimeter, and values of Cp,? were determined with a twin fixed-cell, differential temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results for each compound. Values of Ka, Δ rHm, and Δ rCp,m for the proton ionization reaction of aqueous HIO 3 are calculated and discussed. 相似文献
17.
We determined apparent molar volumes V? at 278.15 ? ( T/K) ? 368.15 and apparent molar heat capacities Cp,? at 278.15 ? ( T/K) ? 393.15 at p = 0.35 MPa for aqueous solutions of tetrahydrofuran at m from (0.016 to 2.5) mol · kg ?1, dimethyl sulfoxide at m from (0.02 to 3.0) mol · kg ?1, 1,4-dioxane at m from (0.015 to 2.0) mol · kg ?1, and 1,2-dimethoxyethane at m from (0.01 to 2.0) mol · kg ?1. Values of V? were determined from densities measured with a vibrating-tube densimeter, and values of Cp,? were determined with a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T for each compound were fitted to our V? and Cp,? results. 相似文献
19.
Apparent molar volumes Vϕ and apparent molar heat capacities Cp,ϕ were determined at the pressure 0.35 MPa for aqueous solutions of magnesium nitrate Mg(NO 3) 2 at molalities m = (0.02 to 1.0) mol · kg −1, strontium nitrate Sr(NO 3) 2 at m = (0.05 to 3.0) mol · kg −1, and manganese nitrate Mn(NO 3) 2 at m = (0.01 to 0.5) mol · kg −1. Our Vϕ values were calculated from solution densities obtained at T = (278.15 to 368.15) K using a vibrating-tube densimeter, and our Cp,ϕ values were calculated from solution heat capacities obtained at T = (278.15 to 393.15) K using a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results, and standard state partial molar volumes and heat capacities were obtained over the ranges of T investigated. 相似文献
20.
Densities of binary mixtures of N,N-dimethylacetamide (DMA) with water (H 2O) or water- d2 (D 2O) were measured at the temperatures from T=277.13 K to T=318.15 K by means of a vibrating-tube densimeter. The excess molar volumes VmE, calculated from the density data, are negative for the (H 2O + DMA) and (D 2O + DMA) mixtures over the entire range of composition and temperature. The VmE curves exhibit a minimum at x(DMA)≅0.4. At each temperature, this minimum is slightly deeper for the (D 2O + DMA) mixtures than for the corresponding (H 2O + DMA) mixtures. The difference between D 2O and H 2O systems becomes smaller when the temperature increases. The VmE results were correlated using a modified Redlich–Kister expansion. The partial molar volume of DMA plotted against x(DMA) goes through a sharp minimum in the water-rich region around x(DMA)≅0.08. This minimum is more pronounced the lower the temperature and is deeper in D 2O than in H 2O at each temperature. Again, the difference becomes smaller as the temperature increases. The excess expansion factor αE plotted against x(DMA) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D 2O + DMA) mixtures than for the corresponding (H 2O + DMA) mixtures, and the difference becomes smaller as the temperature increases. At its maximum, αE can be even more than 25 per cent of total value of the cubic expansion coefficient α in the (H 2O + DMA) and (D 2O + DMA) mixtures. 相似文献
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