| Abstract: | Viscosities of the isomers of pentanol (1-pentanol, 2-pentanol and 3-pentanol) and their binary solutions with toluene in the whole range of composition have been measured at different temperatures between 303.15 and 323.15 K. Viscosities of pure components have been plotted against temperature and for binary mixtures, against the mole fraction of pentanols at different temperatures. At lower concentrations of pentanols, viscosities increase slowly, but at an increasing rate on the continued addition of pentanols in toluene. The excess viscosities and excess free energies of activation for viscous flow are in the order, 3-pentanol + > 2-pentanol + > 1-pentanol + toluene. Excess entropies are found to be negative for the systems 2-pentanol + toluene and 3-pentanol + toluene in the whole range of composition, but for 1-pentanol + toluene the values are small and they are either positive or negative at different compositions. The disruption of H-bonds in pentanols either by thermal effect or by the force of dispersion is in the order: 3-pentanol > 2-pentanol > 1-pentanol. This effect is considered to be quite significant in explaining the temperature dependence of viscosity of pure pentanols, negative excess values of viscosity, free energy and entropy for viscous flow as well as their orders for all the systems. |
