THE JOURNAL OF
PHYSICAL CHEMISTRY (Registered in
U. 9. Patent Office)
VOLUME 63
(0Copyright, 1959, by the American Chemical Society)
NUMBER 9
OCTOBER 1, 1959
THE ENTROPIES OF DILUTION OF STRONG ELECTROLYTES BY ROBERT H. WOOD' Contribution from the Department of Chemistry of the University of California, and the University of Delaware, Newark, Delaware Received October 7 , 1968
The partial molal entropies of dilution of some 1-1 and 2-1 electrolytes have been correlated using a single parameter for each ion. In the case of the negative ions this parameter is very nearly the reciprocal of the ionic radius. For most of the compounds which do not fit the correlation very well, there is other evidence for the abnormal behavior of solutions of these compounds. More data are needed to see whether this correlation is valid for other types of electrolytes.
Introduction At the concentrations above 0.1 rn the deviations of the relative partial molal entropies of dilution of strong electrolytes from the values predicted by the Debye-Huckel equation2 are quite large. This investigation was undertaken to find a correlation of entropies of dilution with some other parameter. It was hoped that such a correlation would shed some light on the reasons for the deviations from the predicted behavior. Calculations.-The integral heats of dilution have been taken from the data of the National Bureau of standard^.^ The relative partial molal heat contents of the salts (12)were computed from the slopes of a graph of the relative heat content vs. the square root of the concentration in moles per kg. of water. The relative non-ideal partial molal free energies and entropies were computed from the activity coefficients4 and 1 2 by means of the equations P* = R T I n ( 7 . t ) ~ and TJ"
=
z2- F E
where RE and SE are the excess (i.e., non-ideal) relative partial molal free energy and entropy. The total number of ions that form when the salt
is dissolved in water is given by Y and y.t is the mean molal activity coefficient. The data are given in Tables I, 11, and 111. Because of the difficulty in measuring the slope of a curve and because of the inaccuracy in some of the data the values of some salts may be in error by 30 calories or more. TABLE I
z,
FOR
Molality HCl
H Br HI
"Os LiOH LiCl LiBr LiNOa NaOH
NaF NaCl NaBr NaI NaNOs NaClOa NaClO4 NaSCN KOH
I
