Coefficient, activity distribution

The stabiHty criteria for ternary and more complex systems may be obtained from a detailed analysis involving chemical potentials (23). The activity of each component is the same in the two Hquid phases at equiHbrium, but in general the equiHbrium mole fractions are greatiy different because of the different activity coefficients. The distribution coefficient m based on mole fractions, of a consolute component C between solvents B and A can thus be expressed... 

From the above dependence, and from the definition of the limiting or activity distribution coefficient of electrolyte, i.e., from the equation ... 

Boltzmann s constant temperature charge of ion distribution coefficient activity coefficient of species i potential at o-plane potential at (5-plane potential at d-plane... 

Solution of the equations is a process in which the coefficients of Eq. (14.28) are iteratively improved. To start, estimates must be made of the flow rates of all components in every stage. One procedure is to assume complete removal of a light key into the extract and of the heavy key into the raffinate, and to keep the solvent in the extract phase throughout the system. The distribution of the keys in the intermediate stages is assumed to vary linearly, and they must be made consistent with the overall balance, Eq. (14.27), for each component. With these estimated flowrates, the values of xik and yik are evaluated and may be used to find the activity coefficients and distribution ratios, Kik. This procedure is used in Example 14.9. 

The values of activity coefficients and distribution ratios are evaluated. 

Both associated and nonassociated electrolytes exist in sea water, the latter (typified by the alkali metal ions U+, Na-, K+, Rb+, and Cs-) predominantly as solvated free cations. The major anions. Cl and Br, exist as free anions, whereas as much as 20% of the F in sea water may be associated as the ion-pair MgF+. and 103 may be a more important species of I than I-. Based on dissociation constants and individual ion activity coefficients the distribution of the major cations in sea water as sulfate, bicarbonate, or carbonate ion-pairs has been evaluated at specified conditions by Garrels and Thompson (19621. 

As a rough approximation (neglecting the activity coefficients), the distribution ratio of a given trivalent metallic cation (DM) can be derived from the logarithm expression of the concentration equilibrium constant Kex ... 

The term on the left hand side of equation (5.28) is constant at a given temperature and pressure, so it follows that aja = constant and, of course aja = constant. These constants are the partition coefficients or distribution coefficients, P. If the solute forms an ideal solution in both solvents, activities can be replaced by concentration, so that... 

Table 1 Descriptive Statistics for the Regression Coefficient (r) Distributions Derived from 423 Data Set (1269) Regressions, Using 14022 Activities...

Calculation of Activity Coefficients from Distribution Coefficient Data... 

The ys are the activity coeflBcients, [A]o is the concentration of the solute distributed in the solvent phase, [A] is the concentration of the solute distributed in the water phase, and K is the extraction coefficient or distribution ratio. When ja/yb approaches 1.0, the analytical concentration of A approaches zero and K approaches D this occurs in dilute solutions. The experimentally determined K remains constant and does not depend upon relative amounts of solutes if ... 

Other names used for the medium effect are solvent activity coefficient (Chapter 6), degenerate activity coefficient and distribution coefficient. 

Maassen, S., Knapp, H., and Arlt, W. (1996) Determination and correlation of Henry s law coefficients, activity coefficients and distribution coefficients for environmental use. Fluid Phase Equilib., 116 (1-2), 354-360. 

As mentioned above, liquid Cd is used as a reaction medium in pyrometallurgical reprocessing. Therefore, for the purpose of designing and optimising the process, it is necessary to accumulate data on the thermodynamic and kinetic properties of actinides in liquid Cd. Many researchers have already reported the thermodynamic properties, such as the activity coefficients and distribution factors of actinides in liquid Cd and molten salts [2-5]. Concerning kinetic properties, the diffusion coefficients of actinide ions in molten salts have been reported [6-9] however, very little is known about the diffusion coefficients of actinides in liquid Cd [10]. 

In SAR work, the biological activity of compounds is usually expressed by the values of IC50 or ED50. Physico-chemical properties used in SAR can be broadly classified into three general tjq)es electronic parameters, steric parameters and hydrophobic parameters. Electronic parameters include Hammett constants o ,(7, <7 ), Swain and Lupton field parameter (F), Swain and Lupton resonance parameter (R), etc. Steric parameters include Taft s steric parameter (Eg), molecular volume (Vm), molecular surface area (Area), molecular weight (MW), van der Waals radius (r), molar refractivity (MR), parachor (Pr), etc. Hydrophobic parameters include partition coefficient (LogP), distribution coefficient (LogD), substituent constant ( ), solubility... 

Concerning the distribution of a drug, models have been published for log BB blood/brain partition coefficient) for CNS-active drugs (CNS, central nervous system) crossing the blood-brain barrier (BBB) [38-45] and binding to human serum albumin (HSA) [46]. 

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