Solute equilibrium constant

The equation just written is generally applicable to any system. The equilibrium constant may be the K referred to in our discussion of gaseous equilibrium (Chapter 12), or any of the solution equilibrium constants (Rw Ra, Rj, K, . . . ) discussed in subsequent chapters. Notice that AG° is the standard free energy change (gases at 1 atm, species in solution at 1M). That is why, in the expression for K, gases enter as their partial pressures in atmospheres and ions or molecules in solution as their molarities. 

LIQUID-PHASE BEHAVIOR. The liquid phase contains dissolved substances and contacts the solid phase. For our purposes, the liquid phase is used synonymously with aqueous phase , and all processes discussed in this section take place in aqueous solutions. The dissolved monomers of the solid phase are formed in equilibrium with their uncomplexed components. Such components may be uncomplexed ions (which are charged atoms or molecules) free in solution or ionic complexes in equilibrium with dissociated ions. Concentrations of the uncomplexed ions, therefore, depend upon the concentrations of all chemical substances competing for binding interactions with them. Each complex-ation reaction is defined by either a solution equilibrium constant ... 

The effect of the medium on the position of equilibrium can be considered from two points of view (a) comparison of the gas-phase and solution equilibrium constants, and (b) comparison of the equilibrium constants for different solvents. Unfortunately, few equilibrium reactions have been studied both in the gas and liquid phases [5, 6j. These are primarily non-ionic reactions where the interaction between reacting molecules and solvent is relatively small e.g. the Diels-Alder dimerization of cyclo-pentadiene). In this chapter, therefore, equilibria which have been examined in solvents of different polarity will be the main topic considered (except for acid-base reactions described in Section 4.2.2). 

Table 4-4. Gas-phase and solution equilibrium constants K-y = [NH]/[OH] of 2- and 4-hydroxypyridine at 25. .. 30 °C unless otherwise stated [65, 67].

IR and UV/Vis [65a], mass spectrometric [65b], photoelectron [65c], microwave [65d], as well as low-temperature matrix-isolation IR spectroscopic measurements [65e] reveal that 2- and 4-hydroxypyridine (as well as 2- and 4-mercaptopyridine [65f]) exist in the gas phase and in inert matrices (N2, Ar) under equilibrium conditions mainly in the lactim (hydroxy or mercapto) form, in contrast to the situation in solution. While in nonpolar solvents such as cyclohexane and chloroform both tautomers exist in comparable amounts, the tautomeric equilibrium is shifted entirely in favour of the lactam (0x0 or thioxo) form in polar solvents such as water, as well as in the crystalUne state [66, 67, 141-145, 251-255], Supercritical-fluid 1,1-difluoroethane can be used to adjust the tautomeric constant Ki = [(llb)]l[(lla)] iso thermally over a continuum from gas-phase values to those measured in polar solvents, simply by increasing the pressure [254]. The gas-phase and solution equilibrium constants of 2- and 4-hydroxypyridine are given in Table 4-4. 

Data for surface complex formation on hydrous ferric oxide (Q) are from Dzom-bak and Morel (5), data for goethite (marked g) are from Sigg and Stumm ( ), and data for y-Al203 ( j are from Kummert and Stumm (8). These data are intrinsic equilibrium constants (i.e., extrapolated to zero surface charge). At the ordinate and abscissa a few relevant surface complex formation constants and solute equilibrium constants, respectively, are listed for which the constants in solution or at the surface are not known they may be used to estimate the corresponding unknown constant. 

M. Arunyanart and L.J. Cline-Love, Model for Micellar Effects on LC Retention Factors and for Determination of Micelle-Solute Equilibrium Constants, Anal Chem., 56 1557 (1984). -... 

Arunyanart M and Cline Love LJ (1984) Model for micellar effects on liquid chromatography capacity factors and for determination of micelle-solute equilibrium constants. Analytical Chemistry 56 1557-1561. 

Surface hydrolysis of metal oxide surfaces can be examined by comparison to solution equilibrium constants for hydrolysis and solubility. Indium oxide has a favorable equilibrium constant for hydrolysis [38-40] ... 

Bromo complexes of Sb(III), Pb(II), and Bi(III) were studied in cationic CTAB/CH2CI2 reverse micelles from the viewpoint of the absorption spectra and coordination number. Since the electronic spectra of the bromomer-curate(II) complexes strongly overlapped with the spectrum of CTAB, these coordination compounds were investigated in the anionic AOT/isooctane micellar system. In some cases, for comparison, spectra were also recorded in homogeneous aqueous solutions. Equilibrium constants were not calculated for the micellar systems because the actual activities of the reactants cannot be determined in the aqueous microphase, although the formal concentrations and ionic strengths may be estimated. 

Co-crystal solubility can be expressed in terms of surfactant micellar concentration, co-crystal and micellar solution equilibrium constants as ... 

The existence of charge transfer complexes of MAH in solution. Equilibrium constants in the range 3 to 60 x lO cm /mol were found at 20 to 30 °C in CHCI3 or hexane for comonomers such as styrene, a-methylstyrene, vinyl acetate, vinyl ethers, or vinyl sulfides [21-23]. 

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