Appendix H: Some Thermodynamic Activity Coefficient Models

• Published in: Kinetic Modeling of Reactions In Foods pp. 755 - 758
• Main Author: van Boekel, Martinus A.J.S.
• Format: Book Chapter
• Language: English
• Published: United Kingdom CRC Press 2009; Taylor & Francis Group
• Subjects: Food & beverage technology; Ln Fi; Short Range Interactions; Laar; Binary System; Nonpolar Systems; GSR; Neutral Solutes; Partial Molar Volume; Long Range Interactions; Flory Huggins Model; Pitzer Model; GLR; Dipole Dipole Interactions; Semiempirical Models; Van Der Waals Forces; NRTL Model; Margules Equation; Excess Gibbs Energies; Group Contribution Model; Davies Model; Van Der Waals; Electrostatic Nature; Mole Fraction; Excluded Volume Interactions
• ISBN: 9781574446142; 1574446142
• DOI: 10.1201/9781420017410-29

The chemical activity of a component can be interpreted as how active a solute in a real solution is compared to an ideal solution. Deviations from ideal behavior arise because of interactions between particles=molecules. There are long-and short-range interactions. Neutral solutes are subject to shortrange interactions, while charged particles are subject to both short-and long-range interactions. Short range means the range does not exceed one or two neighboring particles. Short-range interactions include:. Excluded volume interactions. Dipole-dipole interactions. Dispersion forcesShort-range interactions lead to the notion of pairwise interaction models; short-range interactions are van der Waals forces and dipole-dipole interactions. Long-range interactions are of electrostatic nature. The deviations can be expressed in excess Gibbs energies G and can be decomposed in short range (SR)and long range (LR):Gex ¼ GSR þ GLR (H:1)Empirical and semiempirical models. There is a gap between theoretical models and industrial relevant systems. The theoretical models, for instance to describe activity coefficients, are, more often than not, not directly applicable to real situations. That is why many empirical models have been built to describe real situations. An attempt is often made to connect the parameters used in empirical models to interpretable physical parameters, making these models semiempirical.