Activation parameters of viscous flow of cyclohexylsulfamic acid in aqueous solution

Abstract

The viscosities of aqueous solutions of cyclohexylsulfamic acid were measured up to a mole fraction of solute of 5 × 10 − 3 (0.25 mol dm − 3 ) in the temperature range from 293.15 to 323.15 K. The relative viscosities of dilute solutions were represented by the Jones–Dole equation which takes into account the association of ions. The coefficient A η was calculated from conductivity measurements with theoretical consideration of ion–ion interactions in viscous flow. The values of the coefficient B i referring to the free ions and of the corresponding coefficient B p for the undissociated acid and their temperature derivatives were calculated. The coefficients B i and B p were analysed using a relation between the Jones–Dole and the Einstein equation. Applying Eyring's theory of the transition state, the partial molar Gibbs free energy, entropy and enthalpy of the ionic and undissociated parts of the acid at infinite dilution were obtained and interpreted. From transition state theory, the average molar Gibbs free energy, enthalpy and entropy of the investigated solutions were estimated and the corresponding coefficients B Y (Y = G,H,S) of free ions and of undissociated acid were discussed on the basis of solute–solvent and solute–solute interactions.