Excess conductivities of isobutyric acid plus water binary mixtures near and far away from the critical temperature

The excess conductivities, sigma(E) and excess energy of activation (Delta E-sigma)(E) of electrical conductivity have been investigated by using electrical conductivities measurements for isobutyric acid + water (IBAW) mixtures over the entire range of mole fractions at six different temperatures, both near and close to the critical temperature (0.0555( T-T-c)/K < 13.055). The results were also fitted with the Redlich-Kister equation. This system exhibited very large negative values of sigma(E) and very large positive values of (Delta E-sigma)(E) due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters Delta H-sigma and Delta S sigma have also been calculated, and show that the critical region has an important effect on the electrical conductivity properties.