Activity coefficient single parameter

A number of authors have suggested various mixing rules, according to which the quantity a could be calculated for a measured electrolyte in a mixture, starting from the known individual parameters of the single electrolytes and the known composition of the solution. However, none of the proposed mixing relationships has found broad application. Thus, the question about the dependence of the mean activity coefficients of the individual electrolytes on the relative contents of the various electrolytic components was solved in a different way. 

The Pitzer equation for single electrolytes with the value of parameters collected in several publication may be used as a compact source of activity coefficient data. From the values y° yj. thus obtained, one may calculate, for example, (/, / ) values using Eq. (6.1). 

In this study, a thermodynamic framework has been presented for the calculation of vapor-liquid equilibria for binary solvents containing nonvolatile salts. From an appropriate definition of a pseudobinary system, infinite dilution activity coefficients for the salt-containing system may be estimated from a knowledge of vapor pressure lowering, salt-free infinite dilution activity coefficients, and a single system-dependent constant. Parameters for the Wilson equation may be determined from the infinite dilution activity coefficients. 

The mean ionic and single-ion activity coefficients are conceptually different parameters, but both must conform to the Debye-Hiickel infinite-dilution limit. This theoretical constraint on activity coefficients takes on a particular mathematical form, depending upon the way in which an electrolyte solution is characterized. In a strictly thermodynamic picture of aqueous solutions, the Debye-Hiickel limit can be expressed as follows 9... 

From the chemical point of view, the heart of an equilibrium speciation calculation is the set of conditional stability constants used. These parameters, in turn, require equilibrium constants and single-species activity coefficients (cf. Eq. 1.26). The accuracy and consistency of equilibrium constants arc major concerns in chemical thermodynamics, as discussed in Special Topic I (Chapter... 

Related Calculations. These calculations show how to use vapor-liquid equilibrium data to obtain parameters for activity-coefficient correlations such as those of Van Laar and Wilson. (Use of liquid-liquid equilibrium data for the same purpose is shown in Example 1.20.) If the system forms an azeotrope, the parameters can be obtained from a single measurement of the azeotropic pressure and the composition of the constant boiling mixture. If the activity coefficients at infinite dilution are available, the two parameters for the Van Laar equation are given directly, and the two in the case of the Wilson equation can be solved for as shown in the example. 

PEG-200 and PEG-400. It was shown that the coupling of our Eq. (4) with the Flory-Huggins equation for the activity coefficient of the water in the binary mixed solvent provides an accurate correlation for the gas solubility with a single adjustable parameter. However, the more simple Eq. (2) has a satisfactory accuracy and is recommended because it requires only the gas solubilities in the individual solvents and the molar volumes of the latter. 

Simple cubic equations of state can correlate both VLE and LLE for polymer solutions and blends with a single interaction parameters. They can be combined with an activity coefficient model for predictive calculations using the so-called EoS/G mixing rules. Applications of cubic equations of state to high pressures are so far limited to those shown for the Sako et al. cubic equation of state. 

The group pair parameters are summarized in Table II. Parameters for CH2-CA, CHjj-OH, CH2-MCOO, CH2-KCO, and CHjr-Cl were computer generated by satisfying activity coefficient data (II) for heptane-benzene, heptane-ethanol, hexane-ethyl acetate, heptane-acetone, and heptane-chlorobenzene systems, respectively. In generating the CB2/C1 parameters, previously determined CH2/CA values were used. In order that no more than a single pair of parameters be sought in a given determination, it is important that proper sequence be maintained. 

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