
TY  - JOUR
A1  - Hush, NS 
T1  - The Free Energies of Hydration of Gaseous Ions
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1948
VL  - 1
IS  - 4
SP  - 480
EP  - 494
KW  - 
UR  - https://doi.org/10.1071/CH9480480 
N2  - Values of hydration energies of individual ions have usually been obtained by division of sums of energies of hydration of pairs of ions, and those calculated by different authors are usually mutually inconsistent. &quot; Experimental &quot; figures, whenever these are quoted, have always been obtained by assuming the truth of theoretical equations whose accuracy has not been independently checked. The distinction between free energy of ion/water-molecule interaction and the real free energy of hydration of a gaseous ion is pointed out, and the importance of Klein and Lange's measurement of the Volta-potential Hg/Hg+ (soln.), which makes possible the direct calculation of real free energies of hydration of individual ions, thus providing a check on theoretical values, is emphasized.   Utilizing this value, the equation - &#916;Fh° = - &#916;Ff° + &#916;Fi° + &#916;Fs°- 103.92 z kcal. (where &#916;Fs° is the free energy of formation of the gaseous monatomic element, &#916;Fi°  is the free energy of ionization, &#916;Ff°is the free energy of formation of the aqueous ion, and &#916;Fh° is the real free energy of hydration of the ion, of valency z, at 298.2° K.) is derived from fundamental considerations. By means of this equation, the real free energies of hydration of 49 ions are calculated, using the most reliable data. It is proposed that these be provisionally accepted as standard values. Several subsidiary values for important ions are calculated indirectly. The difference between &#916;Fh° and the free energy of ion/water-molecule interaction is discussed in relation to the surface structure of water : a value of -0.30 v. is derived for the X-potential at the surface of pure water, and it is concluded that at the water/gas interface the positive poles of the surface layer are oriented towards the gas phase. The applicability of a modified Born equation in the calculation of free energies of hydration is discussed, and a modified equation is proposed which yields values of &#916;Fh° for gaseous ions with noble gas structure in excellent agreement with those calculated independently by the method described above. 
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