Heats of dilution of some electrolyte solutions in D2O and comparison of thermodynamic excess functions in D2O and H2O
Abstract
Heats of dilution of LiCl, NaCl, and Nal solutions in D2O have been measured in the range 1 to 3 M to supplement earlier results of Birnthaler and Lange. The solvent isotope effect on the excess enthalpies is much larger than that on the excess free energies found by Frank and Kerwin. The excess entropies in D2O have been calculated from these data and compared with those in water with the result that, within the experimental error, we have Sex (in H2O) -Sex (in D2O) = ksm, where m is the aquamolality (moles of salt per 55.51 moles of solvent). We find Tks = 54 for LiCl, 35 for NaCl, and 35 for NaI, all in units of cal. mole-1 M-1. These results, as well as the solvent-isotope effects on the entropies of solvation, seem to be consistent with the model of aqueous solutions developed by Frank and Evans, Gurney, and Némethy and Scheraga.