Solubility thermodynamic criteria

At equilibrium, the fugacity of a component in the gas is equal to the fugacity of the same component in the liquid. This thermodynamic criterion defines the relationship between the equilibrium concentration of a component in the gas and its concentration in the liquid. The quantity of gas dissolved in a given quantity of solvent at equilibrium conditions is often referred to as the gas solubility. 

The thermodynamic criterion of solubility is based on the free energy of mixing AG, which states that two substances are mutually soluble if AGm is zero or negative. The free energy of mixing for a solution process between a solvent and a polymer is given by the relation... 

The solubility of sulphamethoxypyridazine in ethanol-water mixtures represents a rare kind of drug solubility in an aqueous mixed solvent, because it exhibits two solubility maxima on the curve solubility versus mixed solvent composition (Escalera et al., 1994). It is of interest to verify if such behavior satisfies the thermodynamic consistency criterion. The values of D were calculated using Eq. (11), and... 

There are some who question the usefulness of the Flory-Huggins solubility parameter for problems related to the solubilization of polymers, although it is agreed that it is useful for study of the thermodynamics of dilute solutions. Barton (1975) has referred to literature that cites its shortcomings as a practical criterion of solubility. Some of these are ... 

The fundamental thermodynamic relationships and their consequences are obeyed. This criterion permits the comparison of calorimetric and solubility data. 

The dissolution of solids in liquids arises often in practice because the liquid phase provides a more homogeneous environment for contact between components as well as for chemical reactions. Solids generally have a finite solubility in a liquid solvent. Exceeding the solubility limit produces a two-phase system, a solid in contact with the solution. This problem of solid liquid equilibrium (SLE) is treated by the same general thermodynamics tools developed so far. When the liquid is saturated in the solid component (solute), the solute satisfies the equilibrium criterion. 

These effects are part of the solubility parameters concept. This concept allows to predict compatibility qualitatively (see Section 6.2). Within the framework of the general principles of the thermodynamics of solutions, the numerical evaluation of compatibility implies the evaluation of the value of the free energy (the Gibbs energy) of mixing over the whole range of solution concentration. However, sueh evaluations are difBcult and often excessive for most practical purposes. Therefore, for the estimation of compatibility, it is more convenient to know the value of aity numerical criterion mentioned in the previous subchapters. 

Solubility is defined by the thermodynamic equilibrium of a solute between two phases, which in the context of this chapter are a solid phase and a liquid solution phase.The criterion for equilibrium between coexisting phases is that the temperature, pressure and molar free energies or chemical potentials of each individual species in each phase are equal.For a co-crystal, however, the sum of the molar free energies or chemical potentials of each co-crystal component plays a key role in determining phase equilibria. The molar Gibbs energy of the co-crystal A B in equilibrium with a solution phase is given by ... 

Lipids with suitable HLB are known to spread on the snrface of water to form monolayer films. It is obvious that if the lipid-like molecule is highly soluble in water, then it will disappear into the bulk phase (same as is observed for SDS). Thus, the criterion for a monolayer formation is that it exhibits very low solubility in water. The alkyl part of the lipid points away from the water surface. The polar group is attracted to the water molecules and is inside this phase at the surface. This means that the solid crystal when placed on the surface of water is in eqnilibrium with the film spread on the surface. Detailed analyses of this equilibrium have been given in the literature (Adamson and Gast, 1997 Birdi, 1999 Gaines, 1966). The thermodynamic analysis allows one to obtain extensive physical data of about this system. 

Values of Henry s law constant k =plc, where p is the partial pressure of the solute in the gas above the solution and c is the concentration of the solute) is a quantity frequently apphed in the thermodynamic description of dilute aqueous solutions, which is used in environmental chemistry and atmospheric physics as a major criterion for describing air-water partitioning of solutes at near ambient conditions. It plays amajor role in evaluating the transport of pollutants between atmosphere and aquatic systems, rainwater and aerosols. The octanol-water partition coefficient is a dimensionless number defined as the ratio of the compound s concentration in a known volume of octan-l-ol (Cq) to its concentration in a known volume of water (c ) after the octan-l-ol and water have reached equihbrium. It has been found to be related to water solubility, soil/sediment absorption coefficients and bioconcentration factors of pollutants for aquatic life. The adsorption coefficient normalised to the organic carbon content of the soil (sediment) is a useful indicator of the binding capacity of... 

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