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

The excess partial molar enthalpies of I-propanol were determined in aqueous urea solutions. The total vapor pressures of 1-propanol-urea-H2O were also measured. The numerical analysis applied in a previous paper (J. Phys. Chem. 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 quantities, the interaction functions between a pair of solute molecules were calculated 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 water. I-Propanol molecules modify the hydrogen bond network in the same manner 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 percolation. However, the H2O-mediated interaction between l-propanol solutes is weakened since the hydrogen bond fluctuation responsible for such an interaction is reduced by the presence of urea.