Thermodynamics of transfer of naphthalene and 2-naphthoic acid from water to (water + ethanol) mixtures at T=298.15 K

Abstract Standard thermodynamic functions of transfer of naphthalene and 2-naphthoic acid from water to (water + ethanol) mixtures at T =298.15 K have been determined from solubility measurements at different temperatures. Standard free energies of transfer of both naphthalene and 2-naphthoic acid showed decreasing tendency with the increasing x (EtOH), and the standard entropy and enthalpy of transfer exhibited a change of double peaks with x (EtOH). The Δ tr G 0 of 2-naphthoic acid decreased more rapidly than that of naphthalene when x (EtOH) x (EtOH) >0.746 at T =298.15 K. The double peaks in the curves of standard entropy and enthalpy of transfer illustrated that the microstructure of the series of mixed solvents of (water + ethanol) underwent a variable process from ordered to disordered and then from disordered to ordered. The results mean that there is a relatively ordered structure near x (EtOH)=0.13 in the (water + ethanol) solutions besides the existence of a clathrate structure in the water-rich region.