Gibbs energies aqueous systems

Besides this experimental method, there is a semitheoretical method by which y can be estimated. Assuming Equation 3 to be valid for any value of s and assuming that y is independent of s, we may outline this method as follows. One mole of a coarse crystalline solid consisting of ions A+ and B" is immersed in an aqueous solution. When the large crystal is cut into small pieces, the interface s increases, and the system gains Gibbs energy. This pulverization finally yields the hydrated ions Aaq+ and Ba( ", and the molar surface reaches a value of ... 

Chen CC, Evans LB. A local composition model for the excess Gibbs energy of aqueous electrolyte systems. AIChE J 1986 32 444-459. 

We consider only aqueous solutions here, but the methods used are applicable to any solvent system. The standard Gibbs energy of formation of a strong electrolyte dissolved in water is obtained according to Equation (11.28). In such solutions the ions are considered as the species and we are concerned with the thermodynamic functions of the ions rather than the component itself. We express the chemical potential of the electrolyte, considered to be MVtAv, in its standard state as... 

Consider an aqueous two-phase system containing A, B, C, and solvent H20 in which the reaction A + B = C occurs. The two phases are separated by a membrane, and the membrane is permeable to all four species. The fundamental equation for the Gibbs energy of the a phase is... 

Chen, C-C, et al., A Local Composition Model for the Excess Gibbs Energy of Multicomponent Aqueous Systems, AlChE Annual Meeting, San Francisco, 1984. 

To finalize the development of the aqueous CO2 force field parameters, the C02 model was used in free energy perturbation Monte Carlo (FEP/MC) simulations to determine the solubility of C02 in water. The solubility of C02 in water is calculated as a function of temperature in the development process to maintain transferability of the C02 model to different simulation techniques and to quantify the robustness of the technique used in the solubility calculations. It is also noted that the calculated solubility is based upon the change in the Gibbs energy of the system and that parameter development must account for the entropy/enthalpy balance that contributes to the overall structure of the solute and solvent over the temperature range being modeled [17]. 

The expression for the excess Gibbs energy is built up from the usual NRTL equation normalized by infinite dilution activity coefficients, the Pitzer-Debye-Hiickel expression and the Born equation. The first expression is used to represent the local interactions, whereas the second describes the contribution of the long-range ion-ion interactions. The Bom equation accounts for the Gibbs energy of the transfer of ionic species from the infinite dilution state in a mixed-solvent to a similar state in the aqueous phase [38, 39], In order to become applicable to reactive absorption, the Electrolyte NRTL model must be extended to multicomponent systems. The model parameters include pure component dielectric constants of non-aqueous solvents, Born radii of ionic species and NRTL interaction parameters (molecule-molecule, molecule-electrolyte and electrolyte-electrolyte pairs). 

Example 2.4. Thermodyanmics of COi Dissolution in Water Describe the variations in the entropy, enthalpy, and Gibbs energy with extent of CO2 dissolution for a two-phase system comprising a gas phase and an aqueous phase. Find the equilibrium state. Initially, a liter of gas at 1 atm total pressure contains 2 X 10 mol of CO2. It is brought into contact with a liter of pure water. The dissolution process is... 

As in a thermodynamic system description used for a normal solubility equilibrium calculation, the system contains a gas phase, if considered relevant for the problem at hand, an aqueous solution phase (external to the fibres), and a number of solid phases, which appear either with fixed stoichiometry or as solid solutions. The fibres are described as a separate aqueous phase. The thermodynamic data and stoichiometry for the solute species inside the fibre phase are identical to those describing the species in the external solution volume, with the exception that the charge of the species in the two aqueous phases must be defined separately. This will ensure that, given valid input values, charge neutrality will apply to both aqueous phases individually in the equilibrium composition calculated by Gibbs energy... 

Results of analyzing Gibbs energy of transfer data on the basis of equation (4.9.8) for five alkali metal halides and TATB from water to various non-aqueous solvents are summarized in table 4.11. Acceptable fits to equation (4.9.6) are obtained for these systems, the correlation coefficient r decreasing with increase in the size of the alkali metal cation and halide anion. However, there is a problem in assessing the properties of the fit on the basis of the response factors and p. ... 

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