Ionic heat capacity, aqueous

Criss, C. M. Cobble, J. W. "The Thermodynamic Properties of High Temperature Aqueous Solutions. V. The Calculation of Ionic Heat Capacities up to 200OC. Entropies and Heat Capacities above 200 C" J. An. Chan. Soc., 1964, 86, 5390. 

CRI/COB2] Criss, C. M., Cobble, J. W., The thermodynamic properties of high temperatirre aqueous solutions. V. The calculation of ionic heat capacities up to 200°C. Entropies and heat capacities above 200°C, J. Am. Chem. Soc., 86, (1964), 5390-5393. Cited on page 643. 

During the last feiv years, CRISS and COBBLE (1) have developed a principle of entropy correspondence for aqueous ions which predicts ionic heat capacities over wide ranges of temperature (0 - 300°). The entropy relations can be summarized as ... 

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... 

The mechanisms that affect heat transfer in single-phase and two-phase aqueous surfactant solutions is a conjugate problem involving the heater and liquid properties (viscosity, thermal conductivity, heat capacity, surface tension). Besides the effects of heater geometry, its surface characteristics, and wall heat flux level, the bulk concentration of surfactant and its chemistry (ionic nature and molecular weight), surface wetting, surfactant adsorption and desorption, and foaming should be considered. 

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. 

Heat capacity data for ions in aqueous solution over the temperature range 25-200°C. Such data for ionic species of uranium, plutonium, other actinides and various fission products such as cesium, strontium, iodine, technetium, and others are of foremost interest. 

The Criss-Cobble correspondence principle is useful for aqueous solutions to about 200 °C. At higher temperatures, the heat capacities Cp of ionic solutes such as NaCl26 at constant pressure rapidly become strongly negative and appear to be headed toward infinite negative values on approaching the critical temperature (which, incidentally, is somewhat higher for aqueous electrolyte solutions than for pure water). If, however, we examine the heat capacities Cy of aqueous electrolytes at constant volume,... 

Water. Water long used mainly for aqueous, generally ionic chemistry, more recently became attractive to replace organic solvents particularly under supercritical conditions (see discussion below). It is abundant, easy to purify, not flammable or toxic, and easily available in large quantities, and, therefore, its use is most economical. Product isolation in many cases can be a simple phase separation, and because of its large heat capacity, water offers an easy temperature control. The... 

Another claim for an apparent mean-field behavior of ionic fluids came from measurements of heat capacities. The weak Ising-like divergences of the heat capacities Cv of the pure solvent and CPtx of mixtures should vanish in the mean-field case (cf. Table I). The divergence of Cv is firmly established for pure water. Accurate experiments for aqueous solutions of NaCl... 

The thermodynamic properties of aqueous species are for a one-molal concentration of the species (1 mol/kg of solvent water), which, for relatively insoluble species, may be strictly hypothetical. The thermodynamic properties of dissolved ionic species are based on the assumption that the heat capacity, entropy, A/// and AGf of the hydrogen ion [H+(aq)], all equal zero at all temperatures and pressures in other words, it is assumed that AG/ = AH/ = S° 0 for the hydrogen ion and that AG ° = AH/ = AS/ = 0 for the reaction... 

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. 

This table contains standard state thermodynamic properties of positive and negative ions in aqueous solution. It includes en-thcdpy and Gibbs energy of formation, entropy, and heat capacity, and thus serves as a companion to the preceding table, Standard Thermodynamic Properties of Chemical Substances . The standard state is the hypothetical ideal solution with molality m = 1 mol/kg (mean ionic molality in the case of a species which is assumed to dissociate at infinite dilution). Further details on conventions may be found in Reference 1. 

For example, Marshall and Slusher (1966) made a detailed evaluation of the solubility of ealeium sulphate in aqueous sodium chloride solution, and suggested that variations in the ion solubility product could be described, for ionic strengths up to around 2 M at temperatures from 0 to 100 °C, by adding another term in an extended Debye Hiickel expression. Above 2 M and below 25 °C, however, further correction factors had to be applied, the abnormal behaviour being attributed to an increase in the complexity of the structure of water under these circumstances. Enthalpies and entropies of solution and specific heat capacity were also reported as functions of ionic strength and temperature. 

Ions in aqueous solutions are characterized by several thermodynamic quantities in addition to the molar volumes, heat capacities and entropies discussed above. These are the molar changes of enthalpy, entropy, and Gibbs energy on the transfer of an ion from its isolated state in the ideal gas to the aqueous solution. They pertain also to the dissolution of an electrolyte in water, since they can be considered as parts in a thermodynamic cycle in which the electrolyte is transferred to the gas phase, dissociates there into its constituent ions, which are then transferred into the solution. Contrary to thought processes, as described in Sect. 2.2., it is impossible to deal experimentally with individual ions but only with entire electrolytes or with such combinations (sums or differences) of ions that are neutral. The assignment of values to individual ions requires the splitting of the electrolyte values by some extra-thermodynamic assumption that cannot be proved or disproved within the framework of thermodynamics. However, for a theoretical estimation of the individual ionic... 

The translational motion of the Li ion in water, for instance, speeds up the solvation by ca. 20% by using of the density functional theory (DFT) with some approximation. The computational progress toward ionic solvation has been arriving to discuss the more comphcate area such as heat capacity changes (by a Monte Carlo calculation), surface effects on aqueous ionic solvation (by a Molecular Dynamics). ... 

In some respects, as for example in the aqueous or hydrate melts, water itself may be considered a proper component of the molten mixture. Other terms used for this general group of liquids are ionic liquids, fused salts, and molten or liquid electrolytes. Particularly common are the mixed salts of the alkali metals and alkaline earth metals which find application in the metallurgical industries owing to their excellent thermal and electrochemical stabilities, and good heat capacities. 

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