Activity coefficient determination

The values of the activity coefficients determined at the azeotropic composition can be used to calculate the coefficients in the Wilson equation (or any other of the three-suffix equations) and the equation used to estimate the activity coefficients at other compositions. Horsley (1973) gives an extensive collection of data on azeotropes. 

As with all speciation calculations, the results for the trace metals depend on the values used for the thermodynamic equilibriiun constants and activity coefficients. Determination of these constants is very difficult because direct detection of trace metal species is complicated by their low concentrations and analytical interferences... 

Results for the various binary mixed surfactant systems are shown in figures 1-7. Here, experimental results for the surface tension at the cmc (points) for the mixtures are compared with calculated results from the nonideal mixed monolayer model (solid line) and results for the ideal model (dashed line). Calculations of the surface tension are based on equation 17 with unit activity coefficients for the ideal case and activity coefficients determined using the net interaction 3 (from the mixed micelle model) and (equations 12 and 13) in the nonideal case. In these calculations the area per mole at the surface for each pure component, tOj, is obtained directly from the slope of the linear region in experimental surface tension data below the cmc (via equation 5) and the maximum surface pressure, from the linear best fit of... 

C, from infinite dilution activity coefficient determined by relative GC technique, Bhatia Sandler 1995)... 

The last factor on the right-hand side of eqn.(3.28) is clearly a phase ratio, independent of the solute. Hence, the activity coefficients determine retention in liquid chromatography. In other words, retention is determined by the molecular interactions of the solute with the stationary and with the mobile phase. 

The value of m may be obtained from the solubility of the salt at the specified temperature and T can be derived from the Debye-Httckel equation, if the solution is sufficiently dilute. For more concentrated solutions, 7 may be estimated by extrapolation from activity coefficients determined in more dilute solution, or by comparison with that of a similar salt at the same concentration. 

Infinite dilution activity coefficient determined by varying solvent properties at each temperature. 

Infinite dilution activity coefficient determined from Eq. (18) with calculated at... 

Fig. 1 0.29 Plots of the change in ionic activity coefficients determined by specific ion electrodes against acetamide concentration cam for 0.25 M NaF Na ion activity coefficient ( ) ion activity coefficient (A) mean activity coefficient for NaF( ) [53],...

Experimental measurements show that molecules in highly compressed gases or highly concentrated solutions, especially if electrically charged, abnormally affect each other. In such cases the true activity or effective concentration may be greater or less than the measured concentration. Hence when the molecules involved in equilibrium are relatively close together, the concentration should be multiplied by an activity coefficient (determined experimentally). At moderate pressures and dilutions, the activity coefficient for nonionic compounds is close to unity. In any event, the activity coefficient correction will not be made in the problems in this book. 

Testing the Debye-Hiickel limiting law, the Debye-Hiickel equation and the extended Debye-Hiickel equation has demanded highly accurate experimental activity coefficient determinations. 

Predicting VLEfrom Infinite-Dilution Activity Coefficients Determined from Ebiilliometry... 

ACTIVITY COEFFICIENT DETERMINATION - FROM SUBROUTINE ACTCF... 

The uncertainty in the activity coefficients determined in this way has been estimated to be less than 0.4 per cent. Application of equation (9) usually... 

Activity-coefficient determination by g.l.c. in tertiary systems is closely linked to the study of donor-acceptor complexes amongst other similarities, two nonvolatile stationary liquids are used. The main difficulty in both cases is preferential adsorption of the solute on one of the stationary liquids at the gas-liquid interface. The g.l.c. method of studying complexes through retention volumes (or activity coefficients) was first mentioned by Chalkley and later extended by Purnell. Because of the dramatic effect on the retention volumes of unsaturated hydrocarbons of adding silver nitrate to the stationary liquid solvent, much of the earlier work was done on unsaturated hydrocar bon/Ag+ complexes. " Other systems also investigated in the last few years are alkyl... 

Column 2 is a sinple distillation that can be designed by the methods discussed in Chapter 4. Column 1 is considerably more cortplex, but the bubble-point matrix method discussed in Chapter 6 can often be adapted. Since the system is nonideal and K values depend on the solvent concentration, a concentration loop is required in the flowchart shown in Figure 6-1. Fortunately, a good first guess of solvent concentrations can be made. Solvent concentration will be almost constant in the middle section and also in the bottom section except for the reboiler. In the top section of the column, the solvent concentration will very rapidly decrease to zero. These solvent concentrations will be relatively unaffected by the tenperatures and flow rates. The K values can be calculated from Eq. (2-35) with the activity coefficients determined from the appropriate VLE correlation. Process simulators are the easiest way to do these calculations (see appendix to Chapter 81. 

The activity coefficients determined for C4—Cg normal hydrocarbons in n-hexadecane and n-dotriacontane as solvents taking accoimt of all... 

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