Aqueous systems equilibrium constant derivation

The thermodynamic functions that describe this equilibrium include the equilibrium constant, the enthalpy, the free energy, and the heat capacity. These are all predictable, and can be derived by a variety of routes, each route yielding the same values for the functions. The equation describing the reaction is sufficient to allow for the initiation of all appropriate calculations. In contrast, the rate of the reaction, and the temperature dependence of the rate of the reaction are inherently unpredictable, and require empirical measurement. In particular, the equation describing the reaction stoichiometry cannot, a priori, enable the kinetic equations to be predicted. Detailed knowledge of the reaction mechanism would be required. This distinction between the inherent predictability of equilibrium conditions, and the empirical nature of kinetic conditions, must be borne in mind when considering the phase behavior of aqueous systems. 

To conclude the derived values of log,o K° and their associated uncertainties are based only on the aqueous phase model and the experimental data, and not on the selected values or uncertainties of the AfG° IRT values of Th" or other auxiliary species used in the modelhng. This holds trae for all the other cases where values of equilibrium constants are determined directly from the experimental data. NONLIN-SIT is a comprehensive program that uses ion interaction parameters and chemical potentials of all of the species expected in a given system, but it may be regarded as a method to optimise equilibrium constants, even if it operates v/o AfG°/Rr values. 

In aqueous solutions at pH 7, there is little evidence of complex formation between [MesSnflV)] and Gly. Potentiometric determination of the formation constants for L-Cys, DL-Ala, and L-His with the same cation indicates that L-Cys binds more strongly than other two amino acids (pKi ca. 10,6, or 5, respectively). Equilibrium and spectroscopic studies on L-Cys and its derivatives (S-methyl-cystein (S-Me-Cys), N-Ac-Cys) and the [Et2Sn(IV)] system showed that these ligands coordinate the metal ion via carboxylic O and the thiolic 5 donor atoms in acidic media. In the case of S-Me-Cys, the formation of a protonated complex MLH was also detected, due to the stabilizing effect of additional thioether coordination. ... 

Jaques and Furter [95] derived an equation for the salt effect on the water-vapour equilibrium in binary mixtures which correlates the temperature and the liquid concentration of the three components ethanol, water and salt. The equation has 6 constants. The theory of the salt effect has been discussed by Furter and Meranda [96]. On the basis of simplifying assumptions Sada et al. [97] have established a relation for the calculation of vapour-liquid equilibria for non-aqueous binary systems in which the salt is dissolved only in one component e.g., benzene-ethanol with lithium or calcium chloride). 

In order to understand this isotherm, it is worthwhile to apply Gibbs phase rule (93) which, at constant temperature and pressure, states that the number of degrees of freedom (F) in a system at equilibrium is equal to the number of components (C) in the system minus the number of phases (solid, liquid, gas) present in the system, or F — C — P. Crisp (94) has derived a two-dimensional phase rule to apply to a single plane surface containing q surface phases. The rule predicts that the number of degrees of Freedom (F) will he F = C — Ph — q — ), where C is the total number of components in the system, F is the number of bulk phases, and q is the number of surface phases. In the case of deoxycholic acid spread on aqueous substrate the number of components (C) can be considered to be two, the water of the aqueous phase and the deoxycholic acid. The number of bulk phases, that is the substrate, can be 1 or 2 and the number of surface phases can be 1 or 2. When the area per molecule is very large, for instance 10,000 A- molecule (right side of Fig. 11), the surface pressure is very low (>0.1 dynes/cm) but... 

---