Interactions in 1-propanol-urea-H2O: Chemical potentials, partial molar enthalpies, and entropies at 25 degrees C

The excess partial molar enthalpies of I-propanol were determined in aqueou s urea solutions. The total vapor pressures of 1-propanol-urea-H2O were als o measured. The numerical analysis applied in a previous paper (J. Phys. Ch em. B 1998, 102, 5182) was used to calculate partial pressures and, hence, the excess chemical potentials of each component. Thus, the excess partial molar entropies of l-propanol were obtained. From these partial molar quant ities, the interaction functions between a pair of solute molecules were ca lculated following the method developed by us ( J. Phys. Chern. B 1996, 100 , 5172). All these data seem to indicate that urea molecules lock into the hydrogen bond network of H2O, keep the connectivity of hydrogen bond intact , but reduce the degree of fluctuation that is characteristic of liquid wat er. I-Propanol molecules modify the hydrogen bond network in the same manne r with or without urea, and hence the same amount of 1-propanol is required to break down the connectivity, i.e., the loss of hydrogen bond percolatio n. However, the H2O-mediated interaction between l-propanol solutes is weak ened since the hydrogen bond fluctuation responsible for such an interactio n is reduced by the presence of urea.