Excess chemical potentials, partial molar enthalpies and entropies in binary aqueous acetone and tetramethyl urea at 25 degrees C

We measured excess chemical potentials, mu (E)(i), excess partial molar enthalpy, H-i(E), of solute i in aqueous acetone and tetramethyl urea (TMU). We then evaluated excess partial molar entropy, S-i(E). They all were determined accurately and in small increments in mole fraction, and hence, it was possible to take one more derivative with respect to mole fraction. These higher derivatives were used to learn more about intermolecular interaction in solution. Furthermore, they were used to detect anomalous thermodynamic behaviour, in particular a qualitative change in mixing scheme. We conclude that in both aqueous solutions, three distinctively different mixing schemes are operative depending on the composition range, and that in the most H2O-rich region, solute molecules enhance the hydrogen bond network of H2O in their immediate vicinity. However, the hydrogen bond probability in the bulk of H2O away from solute is reduced. (C) 2000 Elsevier Science B.V. All rights reserved.