Enthalpy Data Research Articles

Excess molar volumes and excess molar enthalpies of binary mixtures for 1,2-dichloropropane + 2-alkoxyethanol acetates at 298.15 K

The excess molar volumes V m E and excess molar enthalpies H m E over the whole range of composition have been measured for the binary mixtures formed by 1,2-dichloropropane (1,2-DCP) with three 2-alkoxyethanol acetates at 298.15 K and atmospheric pressure using a digital vibrating-tube densimeter and an isothermal calorimeter with flow-mixing cell, respectively. The 2-alkoxyethanol acetates are ethylene glycol monomethyl ether acetate (EGMEA), ethylene glycol monoethyl ether acetate (EGEEA), and ethylene glycol monobutyl ether acetate (EGBEA). The V m E of the mixture has been shown positive for EGMEA, ‘S-shaped’ for EGEEA, being negative at low and positive at high mole fraction of 1,2-DCP, and negative for EGBEA. All the H m E values for the above mixtures showed an exothermic effect (negative values) which increase with increase in carbon number of the 2-alkoxyethanol acetates, showing minimum values varying from −374 J mol −1 (EGMEA) to −428 J mol −1 (EGBEA) around 0.54–0.56 mol fraction of 1,2-DCP. The experimental results of H m E and V m E were fitted to Redlich–Kister equation to correlate the composition dependence of both excess properties. In this work, the experimental excess enthalpy data have been also correlated using thermodynamic models (Wilson, NRTL, and UNIQUAC) and have been qualitatively discussed.

A compilation of correlation parameters for predicting the enthalpy and thermal conductivity of solid foods within the temperature range of −40 °C to +40 °C

This paper presents thermal conductivity data for 40 foods, enthalpy data for 58 foods and density data for nine foods, along with the compositions of the foods. Measurements cover a range of solid food types (including meats, fats, offal, fish, dairy products and horticultural products). Some measurements reported are for foods that have never before been studied, others have been published elsewhere, but are included here for convenience. Thermal conductivity was measured using a guarded hot-plate apparatus, enthalpy using an adiabatic calorimeter and density using a water displacement meter. Thermal conductivity and enthalpy values were measured within the temperature range of −40 °C to +40 °C.

Experimental study and ERAS modeling of the excess molar enthalpy of (acetonitrile + 1-heptanol or 1-octanol) mixtures at (298.15, 313.15, and 323.15) K and atmospheric pressure

As a continuation of our studies on excess functions of binary systems, experimental data of excess molar enthalpy ( H m E ) of (acetonitrile + 1-heptanol or 1-octanol) mixtures have been determined as a function of composition at (298.15, 313.15, and 323.15) K at atmospheric pressure using a modified 1455 PARR mixture calorimeter. The H m E is positive for both systems over the whole composition range. The applicability of the ERAS-Model to correlate H m E of the mixtures studied was tested. The agreement between experimental and calculated values is satisfactory.

Synthesis of Submicron Silver Powder by the Hydrometallurgical Reduction of Silver Nitrate with Hydrazine Hydrate and a Thermodynamic Analysis of the System

A silver powder of submicron size was produced from the aqueous solutions of its compounds. The silver compounds tried out were silver nitrate and silver oxide, and the reducing agents employed were dimethyl formamide (DMF), hydrazine hydrate, and sodium azide. The solvent mediums were distilled water for the reductions with DMF and sodium azide, and a 2:1 (by volume) mixture of distilled water and ethanol for the reductions with hydrazine hydrate. Of the three reductants, hydrazine hydrate (N2H4·H2O) alone was successful in reducing both the silver compounds to a submicron (<500 nm) metallic silver powder, as revealed by X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) analyses. Additionally, the thermodynamic equilibrium of the system AgNO3-N2H4·H2O in the water–ethanol mixture (2:1) was studied at 298 K; the equilibrium constant data so generated was found to compare very well with those derived from the established data of enthalpies and free energies of formation, and half-cell potentials. The following activity coefficient (Raoultian)–composition relationship for hydrazine hydrate in its dilute solution in water (plus ethanol) at 298 K is proposed: $$ \ln (\gamma_{{{\text{N}_2\text{H}_4}}{\text{.H}_2\text{O}}} ) = 1862( \pm 371) - 2055( \pm 424)(1 - X_{{{\text{N}_2\text{H}_4 \cdot \text{H}_2\text{O}}}} )^{2} $$

Excess enthalpies of dimethylsulfoxide with substituted benzenes at 298.15 K

Excess molar enthalpies ( H E) at 298.15 K have been measured by a Paar 1451 solution calorimeter as a function of composition for the binary liquid mixtures of dimethylsulfoxide (DMSO) with substituted benzenes. The substituted benzenes include toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene. The H E values for the above mixtures are all positive over the entire composition range. The experimental results have been correlated using the Redlich–Kister (R–K) polynomials. The results are interpreted on the basis of possible hydrogen bonding between unlike molecules and changes in molecular association equilibria as well as structural effects for these systems. The excess enthalpy data have also been correlated with the Peng–Robinson (PR) as well as the Patel–Teja (PT) equations of state (EOS) and also the activity coefficient models of the Wilson and the NRTL.

４f電子雲拡大系列：Ln(III)化合物熱化学データの四組効果とRSPＥT式から求められるラカー・パラメ－ターの大小関係

４f電子雲拡大系列：Ln(III)化合物熱化学データの四組効果とRSPＥT式から求められるラカー・パラメ－ターの大小関係

Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: II. Heat of mixing and activity–composition relationships

The heat of mixing for the binary solid solution diopside–Ca-Tschermak was investigated at T = 980 K by lead borate solution calorimetry. A new statistical technique was applied to overcome the problem of using experimental data of various precisions. A two-parameter Margules model was fitted to the calorimetric data leading to W CaTs–Di H = 31.3 ± 3.4 kJ mol−1 and W H Di–CaTs = 2.4 ± 4.3 kJ mol−1. The results are in good agreement with calorimetric data given in the literature. They agree also with enthalpy data that were extracted from phase equilibrium experiments. With configurational entropy values taken from the literature, the volume and the vibrational entropy, presented in Part I of this work, and the enthalpy data of this study, the activity–composition relationships of the diopside–Ca-Tschermak binary were calculated.

Modeling ferrous–ferric iron chemistry with application to martian surface geochemistry

The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars. The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na–K–Mg–Ca–Fe(II)–Fe(III)–H–Cl–SO 4–NO 3–OH–HCO 3–CO 3–CO 2–O 2–CH 4–H 2O system. The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO 4T = SO 4 + HSO 4) removal; and (3) there was a significantly higher aqueous Cl/SO 4T ratio in the residual Na–Mg–Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars.

Thermophysical properties of the Ni-based alloy Nimonic 80A up to 2400 K, III

Nimonic 80A is a nickel–chromium alloy which is strengthened by additions of titanium and aluminum. The alloy is used for high temperature, high-strength applications. This superalloy is used in gas turbine hot section components, for hot-working applications and forging hammers. This is the third paper reporting thermophysical properties of Nimonic 80A. The optical measurement of temperature is limited by our fast pyrometers with T min = 1200 K for this material and data above about 1200 K have been reported in the previous papers [1,2]. Specific heat capacity data from 500 K up to 1500 K obtained by direct measurement using a differential scanning calorimeter have been used to compute enthalpy as function of temperature. By combining pulse heating and DSC measurements now it is possible to assign a temperature to electrical resistivity and thermal conductivity in the observed temperature range. Thermal conductivity is estimated using the Wiedemann–Franz law. The investigated specific heat capacity, enthalpy, resistivity and thermal conductivity data as function of temperature are presented and compared to literature-values.

Substituent effects on the formation of sulfonyl cations from sulfonyl chlorides: comparisons of solvolysis kinetic data with calculated gas phase energies

AbstractSuitable theoretical methods are validated for organosulfur compounds using experimental data for gas phase enthalpies of formation, proton affinities (PA) and heterolytic bond dissociation enthalpies (HBDEs). From enthalpies of chloride anion transfers from neutral chlorides to acyl, sulfonyl or cumyl cations in the gas phase, it is calculated that (i) similar aromatic substituent effects are expected for heterolyses of acyl, sulfonyl and cumyl chlorides; (ii) HBDEs for loss of chloride increase by over 70 kcal mol−1 from 4‐MeOC6H4COCl to SO2Cl2. Rate constants for solvolyses of 4‐Z‐substituted arenesulfonyl chlorides (Z = OMe, Me, H, Cl, NO2) in 97% w/w 2,2,2‐trifluoroethanol (TFE)–water are reported. Substituent effects are smaller than observed for identical solvolyses of acyl and cumyl chlorides, and are much smaller than those predicted theoretically for gas phase unimolecular heterolysis (explained by variable amounts of nucleophilic solvent assistance). Copyright © 2007 John Wiley &amp; Sons, Ltd.

The activity coefficients of Fe(III) hydroxide complexes in NaCl and NaClO 4 solutions

The osmotic coefficients of FeCl 3 at 25 °C from 0.15 to 1.7 m [Rumyantsev et al., Z. Phys. Chem., 218, 1089–1127, 2004] have been used to determine the Pitzer parameters ( β (0), β (1) and C ϕ ) for FeCl 3. Since the differences in the Pitzer coefficients of rare earths in NaCl and NaClO 4 are small, the values of Fe(ClO 4) 3 have been estimated using the differences between La(ClO 4) 3 and LaCl 3. The Pitzer coefficients for FeCl 3 combined with enthalpy and heat capacity data for the rare earths can be used to estimate the activity coefficients of Fe 3+ in NaCl over a wide range of temperatures (0 to 50 °C) and ionic strength (0 to 6 m). The activity coefficients of Fe 3+ in NaCl and NaClO 4 solutions have been used to determine the activity coefficients of Fe(OH) 2+ in these solutions from the measured first hydrolysis constants of Fe 3+ [Byrne et al., Mar. Chem., 97, 34–48, 2005]. The activity coefficients of Fe(OH) 2 + , Fe(OH) 3 and Fe(OH) 4 - from 0 to 50 °C have also been determined from the solubility measurements of Fe(III) in NaCl solutions [Liu and Millero, Geochim. Cosmochim Acta, 63, 3487–3497, 1999]. These activity coefficients have been fitted to the Pitzer equations. These results can be used to estimate the speciation of Fe(III) with OH − in natural waters with high concentrations of NaCl from 0 to 50 °C.

Excess molar enthalpies of dimethylsulfoxide with chloroethanes and chloroethenes at 298.15 K

Excess molar enthalpies ( H M E ) at 298.15 K and ambient pressure have been measured as a function of composition for the binary liquid mixtures of dimethylsulfoxide (DMSO) with chloroethanes and chloroethenes. The chloroethanes include 1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane and the chloroethenes are trichloroethene and tetrachloroethene. The H M E values for the above mixtures have been measured by a Paar 1451 solution calorimeter and are negative over the whole range of composition in all the binary mixtures except in the binary system of DMSO with tetrachloroethene, whereas the H M E is positive over the entire range of composition. The experimental results have been correlated using the Redlich–Kister (R–K) polynomials and the results are interpreted on the basis of possible hydrogen bonding between unlike molecules and changes in molecular association equilibria as well as structural effects for these systems. The excess molar enthalpy data have also been correlated with the Peng–Robinson (PR) as well as the Patel–Teja (PT) equations of state (EOS) and also the activity coefficient models of the Wilson and the NRTL.

Vaporization Enthalpy: Corresponding-States Correlations Versus DIPPR Database

Data for the vaporization enthalpy accepted in the Design Institute for Physical Property Data® (DIPPR®) database are compared with those given by general correlations based on the corresponding-states method. In particular, four analytical predictive correlations were used. Three of them require as input the critical temperature and the acentric factor. The fourth requires a molecular Lennard-Jones parameter and the acentric factor. Results obtained for 1576 fluids indicate that the recommended model for an overall use, in order to reproduce the DIPPR data, is the one proposed by Sivaraman et al. [Ind. Eng. Chem. Fundam. 23, 97 (1984)].

Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Activation Energy Spectrum Analysis

In the enthalpy relaxation of poly(cyanobiphenyl hexylacrylate) (PCBA6), the decrease in enthalpy was measured as a function of ageing time and ageing temperature in order to analyse it using activation energy spectrum (AES) model. In AES model the decrease in enthalpy is considered to be controlled by molecular processes whose energies are distributed over a continuous spectrum. The relaxation functions were derived from the enthalpy data for four PCBA6 samples of different molecular weights(Mw), then they were verified to obey stretched exponential forms. The relaxation times showed Arrhenius type temperature dependences to give Eapp, apparent activation energies, which became plateau around 200 kJ/mol as the rise in Mw. A plot of reduced ageing times was constructed after the manner of time–temperature reducibility. The fraction of free volume and the thermal expansion coefficient of glass transition were calculated by the method of WLF plot. Then, it was found that these values were relatively large, which is attributable to a property of a side-chain type polymer. AES showed bell-shaped curves; the beginning and the end of the peak were considered to coincide with the lower and the upper limits of activation energies of the relaxation processes, respectively. AES results, such as the area, the height of the peak, the upper and the lower limits, were discussed in terms of the molecular weight and the ageing temperature.

Simultaneous Measurement of Water Desorption Isotherm and Heats of Water Desorption of Proteins Using Perfusion Isothermal Microcalorimetry

The purpose of this work was to study protein-water interactions using a perfusion isothermal calorimetry method by simultaneously measuring the water (de)sorption isotherm and heats of desorption (DeltaH(desorption)). Lysozyme, bovine serum albumin (BSA), and a monoclonal immunoglobulin (IgG) were studied. Desorption isotherms and DeltaH(desorption) were calculated using data from two perfusion systems, which measured heat flow resulting from interaction of water vapor with the protein sample and with pure water, respectively. The desorption isotherms calculated from the calorimetry were in good agreement with the gravimetric data. The average DeltaH(desorption) at high hydration was 54.6 kJ/mol and decreased (approaching heat of water evaporation) with desorption and passed through a minimum at protein specific water content, below which it increased again reaching 59.0 kJ/mol at the lowest hydration levels. The difference between the DeltaH(desorption) above the minimum and heat of water evaporation has been attributed to conformational changes in the protein. This conclusion is supported with data for lysozyme in which a dynamic glass like transition has been observed at the water content of the minimum in the calorimetric enthalpy data at 293 K. This work establishes perfusion calorimetry as a rapid and controlled method to study the thermodynamics of protein-water interaction.

Purification of iridium by electron beam melting

The purification of iridium metal by electron beam melting has been characterized for 48 impurity elements. Chemical analysis was performed by glow discharge mass spectrographic (GDMS) analysis for all elements except carbon, which was analyzed by combustion. The average levels of individual elemental impurities in the starting powder varied from 37 μg/g to 0.02 μg/g. The impurity elements Li, Na, Mg, P, S, Cl, K, Ca, Mn, Co, Ni, Cu, Zn, As, Pd, Ag, Cd, Sn, Sb, Te, Ba, Ce, Tl, Pb, and Bi were not detectable following the purification. No significant change in the concentration of the elements Ti, V, Zr, Nb, Mo, and Re was found following melting. The elements B, C, Al, Si, Cr, Fe, Ru, Rh, and Pt were partially removed by vaporization during electron beam melting. Langmuir's equation for ideal vaporization into a vacuum was used to calculate for each impurity element the expected ratio of impurity content after melting to that before melting. Equilibrium vapor pressures were calculated using Henry's law, with activity coefficients obtained from published data for the elements Fe, Ti, and Pt. Activity coefficients were estimated from enthalpy data for Al, Si, V, Cr, Mn, Co, Ni, Zr, Nb, Mo, and Hf and an ideal solution model was used for the remaining elements. The melt temperature was estimated from measured iridium weight loss and impurity measurements. Good agreement, either quantitative or qualitative, was found between measured and calculated impurity ratios for all impurity elements. The results are consistent with some localized heating of the melt pool due to rastering of the electron beam, with an average vaporization temperature of 3100 K as compared to a temperature of 2965 K calculated for uniform heating of the melt pool. The results are also consistent with ideal mixing in the melt pool.

Extrapolation of VLE data and simultaneous representation of caloric and volumetric properties by means of a cubic 3-parameter equation of state

Simultaneous description of vapour–liquid equilibria and excess enthalpy data in a wide temperature range and the prediction of vapour–liquid equilibrium data at high temperatures and pressures from excess enthalpy data with the help of a single isotherm at a low temperature are investigated by using a cubic 3-parameter equation of state more suitable for process calculations than 2-parameter versions because of a better common representation of vapour pressures, densities and other related data. Two g E-mixing rules in which the NRTL-equation is adopted are used for this purpose. The necessary temperature dependence of the model parameters is studied in detail and the simultaneous representation of the excess volume is examined.

Experimental and theoretically estimated excess molar enthalpies for tert-butyl methyl ether+ 1-pentanol+octane at 298.15 K

Forming part of the scientific project entitled ‘Study on physical properties of mixtures hydrocarbon+alcohol+ether like alternative fuels’, the present article reports experimental data of excess molar enthalpies for the ternary mixture {x1tert-butyl methyl ether (MTBE)+x21-pentanol+(1−x1−x2)octane} and the involved binary mixture {x1-pentanol+(1−x) octane} at the temperature of 298.15 K and atmospheric pressure. No experimental excess enthalpy values were found in the currently available literature for the ternary mixture under study. The group contribution model of the UNIFAC (in the versions of Larsen, and Gmehling) were used to estimate excess enthalpy values. Several empirical expressions for estimating ternary properties from binary results were also tested.

Equilibrium Constants for Isomerization of n-Paraffins

A correlation between lumped isomerization equilibrium constants (Keq) and the number of carbon atoms in paraffinic chains has been developed. The aim of the work is to check the meaningfulness from a chemico-physical point of view of previously estimated values of Keq in order to improve the performances of a simulation model for the isomerization/hydrocracking of Fischer−Tropsch (F−T) waxes, a mixture made up of normal paraffins covering a wide range of molecular weights. Owing to the lack of experimental data for paraffins with more than ten carbon atoms, a procedure has been developed to determine equilibrium constants extrapolating the thermodynamical data of low carbon number paraffins. Since in our case the hydrocracking simulation model considers lumped classes of isomers (i.e., monobranched and multibranched), the equilibrium data do not take into account single isomerization reactions but those from a n-paraffin to the lump of its monobranched isomers and from the lump of monobranched isomers to the lump of multibranched ones. The coherence of the estimated constants has been verified by comparison with the little data available in the literature on lumped equilibrium constants. The analysis of equilibrium constants at different temperatures has shown that isomerization becomes endothermic from a number of carbon atoms equal to about 13−14 onward; this result is also supported by enthalpy data.

The system H 2O–NaCl. Part II: Correlations for molar volume, enthalpy, and isobaric heat capacity from 0 to 1000 °C, 1 to 5000 bar, and 0 to 1 XNaCl

A set of correlations for the volumetric properties and enthalpies of phases in the system H 2O–NaCl as a function of temperature, pressure, and composition has been developed that yields accurate values from 0 to 1000 °C, 1 to 5000 bar, and 0 to 1 X NaCl. The volumetric properties of all fluid phases from low-density vapor to hydrous salt melts and single-phase binary fluids at high pressures and temperatures, can be described by a simple equation V solution ( T , P , X NaCl ) = V H 2 O ( n 1 + n 2 T , P ) i.e., for a given pressure and composition, the molar volume of the solution is related to the molar volume of pure water at the same pressure by a linear scaling of temperature. The parameters n 1 and n 2 are simple functions of pressure and composition. This linear relation could be demonstrated for all ( P, X NaCl) pairs where accurate volumetric data are available over a sufficiently large temperature interval. Extrapolations over as much as 300 °C predict high temperature data within their experimental uncertainty of 1–2%. With a simple fit of parameters n 1 and n 2, the vast majority of several thousand experimental data points from the literature can be reproduced within experimental error, including dilute solutions in the compressible region. Although a strict theoretical foundation is lacking, this behavior can phenomenologically be rationalized as reflecting the relation between the linear to near-linear isochores of binary fluids to those of pure water. Accordingly, small deviations from linearity that amount to 0.1–0.2% error in molar volume occur only at low temperatures where the pure water isochores behave non-linearly. This effect is accounted for by introducing a deviation function. Given its high accuracy, the formulation for the molar volumes could be integrated along isotherms–isobars to generate data for the specific enthalpy of binary solutions. In order to allow direct computation rather than numerical integration, a correlation scheme was developed that is mathematically similar to that for molar volumes. Specific enthalpies computed from the correlation typically agree within 1–3% with those obtained from other studies. Similarly, isobaric heat capacities show good agreement with published data except for high salinities at moderate pressures and temperatures.