Solubility constant, thermodynamic

While the solubility constants for various potential solids can indicate which solid is thermodynamically stable under a given set of conditions, reactions involving precipitation or dissolution of a solid are typically more subject to kinetic limitations than are reactions that take... 

Determining solubility constants in aqueous solutions generally involves analytical work to determine concentrations [ ] or potentiometric measurements to obtain activities. The ratio of activity and concentration—i.e., the activity coefficient and its change with concentration— depends on the choice of the standard state. If pure water is chosen as a standard state, the activity coefficients approach unity only in dilute solutions. It is therefore necessary to express the so-called thermodynamic constants TK (48) in terms of activities. If, on the other hand, one chooses as reference an aqueous solution of comparatively high and constant ionic strength, the activity coefficients remain close to unity even at rather high concentrations of the reacting species. In this case, we may use stoichiometric constants K (48), expressed in molarities, M, and related to a particular ionic medium. 

This procedure enables us to determine the stoichiometric solubility constant. With a little additional information we can calculate the corresponding thermodynamic constant. For this purpose we shall consider a simple cycle ... 

In Figure 5 we have plotted S.I. values for melanterite indicating a trend towards saturation for the Hornet effluent (labeled B). All of the other waters (collected at downstream sites) have been diluted and oxidized and therefore appear undersaturated. The results of these calculations compare quite favorably with field observations. Unfortunately, there is a large uncertainty associated with the thermodynamic solubility constant for melanterite. Although its solubility is well-known, the thermodynamic equilibrium constant is difficult to obtain because the compound is highly soluble and therefore becomes saturated only at high ionic strenths. 

General Considerations. In order to facilitate the discussion of methods for calculating the saturation state of seawater with respect to calcium carbonate, initial consideration will be given to pure calcium carbonate phases. The method most frequently used expressing the saturation state of a solution with respect to solid phase is as the ratio (Q) of the ion activity (a) product to the thermodynamic solubility constant (K). For the calcium carbonate phase calcite, the expression for the saturation state is defined as (e.g., 13) ... 

The thermodynamic solubility constant in pure water ( Tcaco,) is given by... 

Adjustments must be made in the tables of thermodynamic properties to account for new, or better data, while maintaining the overall unity and consistency of these tables. For example, from the NBS Tech. Note 270-series, Selected Values of Thermodynamic Properties,1 a AG° of solution of CaS04 2H20(c) of 5.96 kcal.mol-1 is obtained. This leads to a solubility constant, Ks°, of 4.3 x 10 5 (from equation 3). More recent data indicate a value of AG° = 6.25 kcal mol-1, which results in a K ° = 2.63... 

It must be emphasised, however, that potentiometric measurements are thermodynamically comparable only when exactly the same phases are involved in the respective redox reactions. As shovm in Figure V-11 the solubility constant and consequently the Gibbs energy of formation of P-Ni(OH)2 presumably depends on the particle size (compare thick solid and thick dash curves which differ by 0.8 logioAT-units). Thus the total uncertainty in Equation (V.48) is composed of an experimental random error 2cj 1.5 kJ-mol" and a systematic error due to the solid phase used of 4.5 kJ-moT . 

The solubility data of synthetic NiC03 were thermodynamically analysed to obtain the respective standard molar quantities of formation AjG and A,//". An analogous set of equations was used as described in Section V.3.2.2.3 (Equations (V.41) - (V.44)). Solubility constants were extrapolated to infinite dilution using the Specific Ion-interaction Theory [97GRE/PLY2]. All calculations were based on auxiliary quantities which were either recommended by CODATA (see NEA TDB auxiliary data set) or recently critically evaluated (see Section V.2.1). 

Based on thermodynamic quantities, derived from the experimental investigation of the solubility of nickel sulphide performed by Thiel and Gessner [14TH1/GES], solubility constants as well as Pourbaix diagrams (redox potential plotted V5. pH) have been calculated. 

Constants of Inorganic Substances — This book presents physical constants, thermodynamic data, solubility, reactivity, and other information on over 3000 inorganic compounds. Since it draws heavily on Russian literature, it contains a great deal of data that do not make their way into most U.S. handbooks. (R. A. Lidin, L. L. Andreeva, and V. A. Molochko, Begell House, New York, 1995)... 

VII.4.2.1 Solubility constant of Th02(cr) calculated from thermodynamic data... 

Studies of the speciation of actinides in environmental waters are made difficult by the very low concentrations involved and the possibility that minor, undetected contaminants may dominate the binding of a particular metal ion. The environmental behaviour of the actinides has been reviewed. Americium and thorium exhibit simpler behaviour than other actinides since their oxidation states under such conditions are limited to Am and Th. Both are readily adsorbed by granitic rocks and tend to exhibit low solubilities, The thermodynamic solubility product of amorphous Am(OH)3 has been measured as log = 17.5 0.3 and no evidence for amphoteric behaviour or the formation of Am(OH)4 was found below pH 13. Stability constants for the binding of Am to humic acid have been found to vary with the degree of ionization, a, and were given by log = 10.58a -1-3.84 and log 2 = 5.32a -b 10.42. These were larger than the corresponding values for Eu. Humic acids also bind Th as described in Section 65.2.1. 

The solubility and thermodynamic properties of various gases in [BMIM][PFg] has been determined using a gravimetric microbalance [4]. Essentially, the solubility of CO2 (particularly relevant as a carbon source) was very high, with reasonable solubilities observed for ethylene, ethane, and methane and low solubilities for oxygen, carbon monoxide, and hydrogen (H2 could not be detected). Subsequently, Henry coefficient solubility constants ofhydrogen in [BMIM][BF4] and [BMIM][PFg]... 

Electron Configurations of the Elements Ionization Constants of Acids and Bases Reduction Potentials Solubility Products Thermodynamic Data Vapor Pressures of Water... 

A collection of numerical data covering a relatively large number of quantities used in physical chemistry and thermodynamics, mainly for inorganic species for example acidity constants including those found in non-aqueous solvents, solubility constants and complexation constants. Regarding electrochemistry, you can find the redox potentials for numerous couples, the molar conductivities for the main ions in aqueous solution, the activity coefficients for electrolytes, as well as a small number of kinetic features (exchange current density, and transfer coefficient, etc.). 

It is important to remember thermodynamic properties or in particular the solubility constants, besides the energy involved and verify if the process is thermodynamically possible. Very important is the precipitation kinetics and how far it is from the equilibrium which influences the precipitation rate. 

Permeability P) is a measure of the amount of gas that passes through a film of thickness I and axea A within a finite amount of time f. It is the result of two distinct processes (i) initially penetrant molecules must dissolve into the surface of the film through a process governed by solubility, and (ii) these molecules must then diffuse across the film to the other surface. In order for permeation to occur, these two mechanisms—one thermodynamic (solubility) and the other kinetic (diffusion)— must both occur [14], Permeability is related to the solubility constant S and diffusion coefficient D by ... 

The permeability of a system represents the amount of gas passing through a material specimen with cross-sectional area A and thickness d in a specific unit of time t. The process involves two basic mechanisms, namely, thermodynamic solubility of the permeant in the surface of the films and kinetic diffusion of the permeating molecules across the film to the other surface (Shields, 2008 Gonzo et al., 2006 Robeson, 2003 Kamal and Jinnah, 1984). Thus, permeability can be expressed as a product of solubility constant S and diffusion coefficient D, P = S x D. 

There are two formulations by which stability or solubility constants can be expressed (see Section 2.1). The first is as a stoichiometric constant where the concentrations of the reacting and produced species are utilised. The second and more important formulation is as a thermodynamic constant where the activities of the species are used. An activity is the product of the concentration and the corresponding activity coefficient, and it is essential to understand models developed for determining activities as well as methods for deriving activity coefficients. Using derived activity coefficients, stoichiometric stability or solubility constants can be used to calculate the thermodynamic constants at the standard state, that is, at infinite dilution and a temperature of 25 °C and pressure of 10 Pa. The majority of critical reviews of the stability or solubility constants of metal hydroxide species and phases have derived thermodynamic stability constants. 

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