Excess partial molar enthalpy of 1-propanol in 1-propanol–acetone (or tetramethyl urea)–H2O at 25°C: effect of acetone (or tetramethyl urea) on H2O

Excess partial molar enthalpies of 1-propanol, H1PE, were measured at 25°C in ternary 1-propanol–acetone (or tetramethyl urea)–H2O, with various initial compositions of acetone (or tetramethyl urea). They were determined accurately and in small increments in mole fraction of 1-propanol. It was therefore, possible to take a derivative of H1PE with respect to the amount of 1-propanol, n1P, H1P–1PE≡N(∂H1PE/∂n1P). The changes in the mole fraction dependence of H1PE and hence, H1P–1PE caused by adding a third component, acetone or tetramethyl urea, were compared with the results of analogous earlier studies with urea and 2-propanol as a third component. The effects of acetone and tetramethyl urea were found qualitatively the same. The CH3 group in each compound works as a typical hydrophobic moiety and enhances the hydrogen bond network of H2O in the immediate vicinity of solute molecule (“iceberg formation”) with concomitant reduction of the hydrogen bond probability of H2O. The CO group on the other hand, seems to reduce the degree of fluctuation in the hydrogen bond strength in the bulk H2O away from the solute.