Heat capacity aqueous salt solutions

The techniques used in the critical evaluation and correlation of thermodynamic properties of aqueous polyvalent electrolytes are described. The Electrolyte Data Center is engaged in the correlation of activity and osmotic coefficients, enthalpies of dilution and solution, heat capacities, and ionic equilibrium constants for aqueous salt solutions. 

The ionization potentials of some of the bipyridines have been investigated. Solubility data for 2,2 -bipyridine in aqueous solution, in aqueous solvent mixtures, and in various aqueous salt solutions have been obtained, whereas the heat of solution, heat capacities, and related data for 2,2 - and 4,4 -bipyridines in water have been measured. The enthalpies of solution of 2,2 -bipyridine in water and aqueous solvent mixtures have also been obtained. Dielectric relaxation studies of 2,2 -bipyri-dine in carbon tetrachloride have been reported in connection with hindered internal rotation. Partition coefficients for 2,2 -bipyridine between water and various organic solvents have been measured. ... 

Thus the partial molar enthalpy of Bu4N+Br increases sharply when t-butyl alcohol is added to aqueous solutions until x2 - 0 1 and then decreases slowly (Mohanty et al., 1971). Similar complex patterns emerge in the enthalpies of these salts when amide cosolvents are added, e.g. formamide (de Visser and Somsen, 1974a,b). Striking changes are observed in the partial molar heat capacities of salts in TA mixtures when x2 is varied (Avedikian et al., 1975). Thus for Am4N+Br in t-butyl alcohol + water mixtures (Mohanty et al., 1972), the partial molar heat capacity increases as x2 increases to a maximum near x2 — 0-04, drops sharply to a minimum and then... 

The above-mentioned method was initially developed for measuring the isobaric heat capacities of aqueous salt solutions up to 573 K and 30 MPa. For a typical run, the sample cell was loaded with the sample solution and the reference cell was loaded with a reference fluid of known heat capacity (usually water). Then, the temperature was increased from to T, at constant pressure, and the difference Q in the transferred heat was corrected taking into account both the cell s volumetric dissymmetry and the differences between the densities and specific heat capacities of the measured sample and reference fluids, respectively. Such an experiment allows the measurement of the product pCp representing the isobaric heat capacity divided by volume. In order to obtain the desired isobaric heat capacity, Cp, of the solution, it was necessary to know its density. For this purpose, the isobaric specific heat capacity and density were represented by polynomials in terms of temperature T ... 

The second peak occurs in a condition close to the critical line. This peak is not expected to be a result of hysteresis since no new phase is nucleating instead, it has the lambda-like shape typical of the isochoric heat capacity of a pure fluid near its critical point. The analysis of these data will allow a first detailed look at the enviionment of a V-L-S critical end point in an aqueous salt solution. 

Table V-3 Partial molar heat capacity values for Ni(II) salts in aqueous solution at...

This is probably the most comprehensive set of heat capacity results available for any nickel salt in aqueous solution. Apparent molar heat capacities of aqueous Ni(C104)2 were measured calorimetrically from 25 to 85°C over a molality range of 0.02 to 0.80 moFkg. Standard molar heat capacities of Ni for the same temperature range were obtained by using the additivity rule and data for HC104(aq), given in literature. The results for C° (Ni " ) can be fitted with a conventional heat capacity model valid from... 

A single homogeneous phase such as an aqueous salt (say NaCl) solution has a large number of properties, such as temperature, density, NaCl molality, refractive index, heat capacity, absorption spectra, vapor pressure, conductivity, partial molar entropy of water, partial molar enthalpy of NaCl, ionization constant, osmotic coefficient, ionic strength, and so on. We know however that these properties are not all independent of one another. Most chemists know instinctively that a solution of NaCl in water will have all its properties fixed if temperature, pressure, and salt concentration are fixed. In other words, there are apparently three independent variables for this two-component system, or three variables which must be fixed before all variables are fixed. Furthermore, there seems to be no fundamental reason for singling out temperature, pressure, and salt concentration from the dozens of properties available, it s just more convenient any three would do. In saying this we have made the usual assumption that properties means intensive variables, or that the size of the system is irrelevant. If extensive variables are included, one extra variable is needed to fix all variables. This could be the system volume, or any other extensive parameter. 

For dilute aqueous solutions of inorganic salts, a rough estimate of the specific heat capacity can be made by ignoring the heat capacity contribution of the dissolved substance, i.e. 

The solubilities of the scale-forming salts barium and strontium sulphates in aqueous solutions of sodium chloride have been reviewed by Raju and Atkinson (1988, 1989). Equations were proposed for the prediction of specific heat capacity, enthalpy and entropy of dissolution, etc., for all the species in the solubility equilibrium, and the major thermodynamic quantities and equilibrium constraints expressed as a function of temperature. Activity coefficients were calculated for given temperatures and NaCl concentrations and a computer program was used to predict the solubility of BaS04 up to 300 °C and SrS04 up to 125 °C. 

APPARENT MOLAL HEAT CAPACITIES OF AQUEOUS SOLUTIONS OF ALKALI HALIDES AND ALKYLAMMONIUM SALTS. 

The solubility product Ksp can be calculated for a given temperature, as in the case of a typical chemical reaction, using the tabulated standard thermodynamic properties of formation for the Gibbs energy and enthalpy and the molar heat capacity of the salt and the ions in aqueous solution (aq). 

Aqueous ions heat capacity, osmotic coefficient, entropy The heat capacities and osmotic coefficients of aqueous solutions of some salts of most of the ions have been determined by Spedding and others (Rard 1985,1987). 

From heat capacities of electrolytes, limiting ionic heat capacities C° [R (aq)] can be derived. Since there have been no parallel measurements for aqueous solutions of salts of any actinide ions An no comparisons can be made, although estimates have been... 

Factors Affecting Stability to Heat Plasma and serum are notable for their capacity to hold in stable aqueous solution many substances whose solubility in pure water or salt solutions is extremely low. The remarkable capacity of certain globulin fractions— notably those from Fractions III-O and IV-1, as separated by the low temperature-ethanol technique— to bind cholesterol, phos-phatides, and other types of lipid material, in stable, water-soluble combination has already been described in the preceding section. Serum albumin, however, displays equally remarkable afiSnities for a somewhat different and extremely diverse group of substances, including many types of acid and basic dyes, the ions of many organic acids containing hydrocarbon residues, certain quinone derivatives, and other substances. 

Crea F, De Stefano C, Millero FJ, Sharma VK (2004) Dissociation constants for citric acid in NaCl and KCl solutions and their mixtures at 25 °C. J Solut Chem 33 1349-1366 Patterson BA, Wooley EM (2001) Thermodynamics of proton dissociations from aqueous citric acid apparent molar volumes and apparent heat capacities of citric acid and its sodium salts at the pressure 0.35 MPa and at temperatures from 278.15 to 393.15 K. J Chem Thermo-dyn 33 1735-1764... 

Rard, J.A. and F.H. Spedding, 1974, A Survey of Some Properties of Aqueous Rare Earth Salt Solutions. II. Heats of Dilution, Heat Capacities, Activity Coefficients, Electric Conductances, and Relative Viscosities, in J.H. Haschke and H.A. Eick, eds.. Proceedings of the 11th Rare Earth Research Conference, (Tech. Inform. Center, Oak Ridge, Tenn.) p. 919. 

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