Solubility of xenon in 45 organic solvents including cycloalkanes, acids, and alkanals: Experiment and theory

Abstract

New measurements are reported of the Ostwald solubility L(T), as a function of temperature in the approximate range 10.0–50.0 °C, for 133Xe gas in 13 liquid organic solvents, viz., three cycloalkanes, six carboxylic acids, and four normal alkanals. From our data for each solute–solvent system we determine the mole-fraction solubility x2(T), and the following thermodynamic functions of solution: chemical potential Δμ0ρ2(T)=−RT ln L, enthalpy ΔH̄0ρ2, and entropy ΔS̄0ρ2, where Δμ0ρ2=ΔH̄0ρ2 −TΔS̄0ρ2S̄0ρ2, all based on the number density scale. New results are considered together with previous measurements of xenon solubility in liquid normal alkanes, alkanols, and perfluoroalkanes; in all, data and theory are treated for xenon solubility in 45 organic solvents from six homologous series. The average observed entropy of solvation of Xe is ΔS̄0ρ2=−4.1± 0.5 cal/mol K, remarkably independent of solvent. The results are analyzed with scaled-particle theory from which are obtained hard-core diameters a1, and cavity energies gcav and enthalpies hcav for all the solvents at 25 °C. Values of a1 range from 4.08 Å (for CH3OH) to 9.18 Å (n-C20H42), and gcav ranges from 2520 cal/mol (n-C6F14) to 9430 cal/mol (HCOOH). We discuss the application to solubility in these solvents of interaction site calculations; interaction potentials for the functional groups are available but difficult to apply to these solute–solvent systems. We also discuss the role of configurational entropy, as well as molecular dynamics approaches to calculation of free energies of solubility. Finally the results are examined empirically and values are given for the contribution to chemical potential, enthalpy, and entropy of solvation, of the six functional groups: CH2 (linear molecules), CH3, OH, COOH, CHO, and CH2 (cyclomolecules).