Excess thermodynamic properties of the binary liquid system ethylene glycol-methanol

Abstract

The excess thermodynamic properties of the binary liquid system, ethylene glycol-methanol, have been determined at 25°C. It has been demonstrated that this system (1) Shows small, but definitely positive, deviations from Raoult's Law, the excess Gibbs energy having a maximum value of about 55 cal. mole�¹ at 55 mole per cent methanol. (2) Is slightly endothermic upon mixing, the maximum excess enthalpy being positive by approximately 32 cal. mole�¹ at 55 mole per cent methanol. (3) Undergoes a small contraction in volume upon mixing, the minimum excess volume being ca. -0.65 ml. mole�¹ at 60 mole per cent methanol. (4) Exhibits a negative excess entropy, the minimum Ts(superscript E) being about -24 mole�¹ at 50 mole per cent methanol. An explanation has been offered to account for the positive deviations from Raoult's Law on the basis of molecular clustering, or "molecular nepotism." It has been postulated that the positive h (superscript E) arises from breaking and forming hydrogen bonds of different types. The small contraction in volume is thought to arise from the structural changes of the two components upon mixing. No adequate explanation can be given for the sign or magnitude of the excess entropy, although a number of contributing factors are considered.