Concentrated electrolyte solutions thermodynamics

Perron G, Hardy A, Justice J-C, Desnoyers JE (1993) Model system for concentrated electrolyte solutions thermodynamic and transport properties of ethylammonium nitrate in acetonitrile and in water. J Solutitm Chem 22 1159-1171... 

KON/FAN] Konnecke, T., Fanghanel, T., Kim, J. I., Thermodynamics of trivalent actinides in concentrated electrolyte solutions. Modelling the chloride complexation of Cm(IlI), Radiochim. Acta, 76, (1997), 131-135. Cited on page 607. 

To calculate gas solubility in natural geochemical systems, basic thermodynamic properties such as the Henry s law constant and, in the case of weak electrolytes the dissociation constant, must be combined with a thermodynamic model of aqueous solution behavior. An analogous approach has been used to predict mineral solubilities in concentrated brines (1). Such systems are also relevant to the atmosphere where very concentrated solutions occur as micrometer sized aerosol particles and droplets, which contain very small amounts of water relative to the surrounding gas phase. The ambient relative humidity (RH) controls solute concentrations in the droplets, which will be very dilute near 1(X)% RH, but become supersaturated with respect to soluble constituents (such as NaCl) below about 75% RH. The chemistry of the aerosol is complicated by the non-ideality inherent in concentrated electrolyte solutions. 

Both the above phenomena are particularly striking when working with concentrated electrolyte solutions they are definitely of a thermodynamic, rather than kinetic, nature and, therefore, must be valid not only under chromatographic (dynamic) conditions but also under static equihbrium conditions. 

Nevertheless, the most rigorous, thermodynamically complete understanding of ion mobility or diffusivity in concentrated electrolytic solutions is provided by the extended Stefan-Maxwell transport theory, which can be applied to electrolytic solutions [13, 17-22], ionic melts or ionic liquids [23, 24], and ion-exchange membranes [25-28]. The diffusion driving force in any system involving ion transport is taken to be a gradient of electrochemical potential /i, typically expressed in terms of a chemical part and an electrical part as... 

Special attention in Chapter 4 (Electrical Conductivity in Hydrothermal Binary and Ternary Systems, H. R. Corti (Argentina)) is paid to the procedures for obtaining information on the thermodynamic properties of electrolytes (including a determination of the limiting conductivity and association constants) from the measured electrical conductivity of diluted solutions above 200 °C. However, the behaviour of specific and molar conductivity in concentrated electrolyte solutions is also carefully discussed in the chapter. 

Concentrated electrolyte solutions are the intermediate materials of many industrial chemical and hydrometallurgical processes. The water of salt lakes and some underground water are also concentrated electrolyte solutions. Therefore both the chemical or metallurgical engineers and geochemists concern the thermodynamic properties of concentrated electrolyte solutions. 

The regularities and estimation methods of the activity coefficients of concentrated electrolyte solutions have been investigated for many years, but up to now these problems are not completely solved yet. In this field, Pitzer s ion-ion interaction model [109], as a semi-empirical model, has been most widely used. In Pitzer s method, the thermodynamic function (such as logarithm value of activity coefficient, log y ) is expanded into a series, and the coefficients of the terms of this series, and P and C, are used to calculate the activity coefficients of solutions of different concentrations. The coefficients P ° P and C have to be calculated from the experimental data of activity coefficients of concentrated... 

Eanghanel, T., Kim, J.I., Paviet, P, Klenze, R., and Hauser, W. (1994) Thermodynamics of radioactive trace elements in concentrated electrolyte solutions hydrolysis of Cm " " in NaCl-solutions. Radiochim. Acta, 66167, 81-87. 

Our present understanding of the thermodynamics of HNO3/H2SO4/ H2O ternary solutions under stratospheric conditions still depends to a high degree on predictions made by thermodynamic models, which allow to calculate the properties of non-ideal, i.e. highly concentrated, electrolytic solutions. The interactions between the species in such solutions are expressed in terms of activity coefficients (/). For example, the solubility of a species HX which dissolves and dissociates in solution can be calculated according to... 

As it is perfectly known, room temperature molten salts or ionic liquids (ILs) are charged complex fluids formed exclusively by ions. They can be seen as an infinitely concentrated electrolyte solution, and one can think about these systems as the opvposite limit to that of the applicability of the DH theory of ions solutions. It is well-known that a polar network exists in these systems, as can be seen for example in (Wei Jiang et al., 2007), so, from the theoretical perspective, one expects that a pseudolattice model is particularly well adapted to the peculiarities of ILs. Indeed, Turmine and coworkers (Bou Malham et al., 2007 Bouguerra et al. 2008) proved that the so called Bahe-Varela (BV) pseudolattice theory of electrolyte solutions is capable of accoxmting for the thermodynamic properties of binary and ternary mixtures of ILs up to the limit of pure IL. 

In electrolyte solutions, nonideality of the system is much more pronounced than in solutions with uncharged species. This can be seen in particular from the fact that electrolyte solutions start to depart from an ideal state at lower concentrations. Hence, activities are always used in the thermodynamic equations for these solutions. It is in isolated instances only, when these equations are combined with other equations involving the number of ions per unit volume (e.g., equations for the balance of charges), that concentrations must be used and some error thus is introduced. 

The concentration overpotential i/c is the component of the overpotential due to concentration gradients in the electrolyte solution near the electrode, not including the electric double layer. The concentration overpotential is usually identified with the Nernst potential of the working electrode with respect to the reference electrode that is, the thermodynamic electromotive force (emf) of a concentration cell formed between the working electrode (immersed in electrolyte depleted of reacting species) and the reference electrode (of the same kind but immersed in bulk electrolyte solution) ... 

This latter expression allows us to compute all the excess properties of dilute electrolytic solutions for instance, the excess osmotic pressure is determined by Eq. (138). The most remarkable result is of course that all these thermodynamic properties are non-anaiytic functions of the concentration ... 

Cruz, Jose-Luis and H. Renon, "A New Thermodynamic Representation of Binary Electrolyte Solutions Nonideality in the Whole Range of Concentrations," AIChE J., 1978, 24, 817. 

When a 60 MW turbine at Hinkley A power station disintegrated in 1969 from stress corrosion cracking of a low pressure turbine disc (consequences shown in Plate 1) it was considered that Na H solutions were most probably involved (84) and it was soon found that if NaOH were the sole electrolyte present its maximum concentration (based on vapour pressure depression) was sufficient to have caused the cracking. However, it was also found that in mixtures it was only the free NaOH which led to rapid stress corrosion cracking. Considerations of acid gas solubility and solution thermodynamics showed that at the CO2 and acetate levels present it was most unlikely that free NaOH was present in sufficient quantity to be responsible for the Hinkley failure (85). 

SOLUTION BEHAVIOR. Biomineralization is dominated by physical chemical considerations , and we begin with a discussion of real electrolyte solutions in which the concentration of a substance exceeds its thermodynamically defined solubility. In such a case, the presence of a coexisting crystal surface will lead to crystal growth. 

The electrolyte is usually 20-28% aqueous solution of KOH. Solid-state compositions of KOH aqueous electrolyte obtained by addition of poly(ethylene oxide) [345] or polymer based electrolyte (based on polyacrylates) were also proposed [346]. For low temperature applications, higher concentrations of KOH were used, while for higher temperatures, sodium hydroxide was sometimes applied. The influence of the temperature from 0 to 200 °C, pressure and electrolyte concentration on the thermodynamic parameters of the cells, was studied in detail [347]. 

The superscript 0 in Eq. 2.2 indicates a true thermodynamic equilibrium constant. We use plain K when concentrations replace activities or, for electrolyte solutions, when K refers to a nonzero ionic strength (see Section 2.2). 

The great increase in complexity in solution thermodynamics which occurs when a salt is dissolved to substantial concentration in a mixture of two liquid components becomes fully apparent in the realization that the liquid phase so created is a concentrated solution of an electrolyte whose degree of dissociation is a function of the relative proportions of the other two components present, and... 

In thermodynamic treatments of electrolyte solutions, one defines an electrochemical potential of a species at a uniform concentration c and potential 0 by... 

Chapter 18 describes electrolyte solutions that are too concentrated for the Debye-Hiickel theory to apply. Gugenheim s equations are presented and the Pitzer and Brewer tabulations, as a method for obtaining the thermodynamic properties of electrolyte solutions, are described. Next, the complete set of Pitzer s equations from which all the thermodynamic properties can be calculated, are presented. This discussion ends with an example of the extension of Pitzer s equations to high temperatures and high pressures. Three-dimensional figures show the change in the thermo-... 

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