Strong and Weak Electrolyte Solutions: Modeling and Classification

Understanding electrolyte thermodynamics is essential for modeling processes in chemical engineering and the natural sciences. This thesis presents a comprehensive study on the modeling and classification of strong and weak electrolyte solutions using a combination of classical and modern theoretical approaches. The core objective is to investigate the fundamental interactions necessary for electrolyte modeling, examining their parametrization and interplay, ultimately leading to a new classification scheme for electrolytes. For strong electrolytes, the work revisits and critically evaluates the Debye-Hückel theory, highlighting its limitations and proposing refinements that incorporate dielectric constant variations and alternative derivation pathways. Ionsolvent interactions are addressed in detail, and improvements to commonly used theoretical treatments are proposed. Charging processes used to derive ionion and ionsolvent contributions to thermodynamic properties are analyzed, and a refined charging framework is introducedbridging the Güntelberg and Debye charging procedures while ensuring thermodynamic consistency. For weak electrolytes, new derivations for ion pairing are presented based on the PoissonBoltzmann equation. It is shown that ion pairing naturally emerges from the nonlinear form of the equation and is essentially lost when the linear DebyeHückel limit is taken. A final major contribution is the development of the Interaction Balance Theory (IBT), which decomposes activity coefficients into attractive/repulsive, short-/long-range, and saltsalt/saltsolvent contributions. This framework enables a physically grounded classification of electrolytes based on dominant interaction regimes, and is demonstrated through the analysis of representative salts. The theoretical tools developed in this work provide deeper physical insight and improved predictive capabilities, supporting more accurate electrolyte modeling in both industrial and scientific contexts.