The thermodynamics of solvation of ions. Part 3. - The heat capacity for solvation of gaseous ions in methanol at 298.15 K

Literature values of the standard partial molar heat capacities of 1:1 electrolytes in methanol have been divided into ionic contributions using the assumption that C̄_p^∞(Ph⁴As⁺) = C̄_p^∞. Combination with C_p^o values for gaseous ions then leads to single-ion values for the solvation of gaseous ions in methanol, Δ_solv C_p^o. These latter values are then broken down into a neutral term N, an electrostatic term E and a configurational term C. It is shown that the above single-ion division leads to configurational single-ion quantities that agree well with other single-ion parameters. Using this division, all the inorganic cations and anions can be regarded as structure-makers that decrease the fluidity of the solvent. The tetra-alkylammonium ions are also structure-makers, but exhibit 'solvophobic solvation', analogous to, but quantitatively much smaller than, the corresponding hydrophobic hydration in water.