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Ranjana Bhattacharyya, Sujit Chandra Lahiri

Examination of the Validity of the Ionic Additivity Principle in the Determination of Single Ion Thermodynamic Properties

Keywords: Additivity Principle, Compensation Effect, Single Ion Thermodynamics, Hydration or Solvation, Entropy of Single Ions

Single ion thermodynamic values of hydration or solvation (or solution) cannot be experimentally determined. The values are determinable from the thermodynamics of solvation ΔX⁰_{solv or soln}(MX) [X = H, G or S] based on ionic additivity and using extrathermodynamic assumptions.

However, the principle of ionic additivity is not valid in the determination of single ion thermodynamic values [i.e. ΔG⁰_solv(M⁺ or X⁻) or ΔG⁰_soln(M⁺ or X⁻), ΔH⁰_solv(M⁺ or X⁻) or ΔH⁰_soln(M⁺ or X⁻)] but additivity principle appears to be valid for the determination of ΔS⁰_{solv or soln}(M⁺ or X⁻).

Moreover, appropriation of ΔG⁰_solv or ΔH⁰_solv(MX) equally on the basis of equality of radii of cations and anions is also not tenable due to differences in the effective charges of the cations and anions of equal radii.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 220, 09/2006
Pages: 1115 - 1124

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