Thermodynamics and Fluctuation Solution Theory with Some Applications to Systems at Near- or Supercritical Conditions

Abstract

The first sections (1–3) give some general thermodynamic analyses of fluids, with representative applications involving near-critical systems. Thorough discussion is given of standard states for phase equilibria and results for various sets of independent thermodynamic variables such as in the Lewis-Randall, Kirkwood-Buff and McMillan-Mayer systems. Differences with sets of composition variables based on species and groups for systems with “reactive” components are illustrated. The second portion (Sections 4–8) describes the fundamentals and applications of fluctuation solution theory (FST) to correlate and predict thermodynamic properties of mixtures. This analysis includes a variety of relations from molecular theory and the behavior of integrals of molecular correlation functions for mixtures, including near-critical conditions. The emphasis is placed on activity coefficients and high dilution partial molar volumes of supercritical substances and salts in liquids at extreme temperatures and pressures. Comments are made about the insight that FST formulations can provide for critical-region systems. FST properties show relatively simple behavior over wide ranges of conditions.