Similarity degrees and differences of argon, hydrogen sulphide, water, methanol and ethanol on their coexistence curves

Abstract

The work is devoted to the analysis of the temperature dependences for the specific volumes and thermal expansion coefficients for water as well as methanol and ethanol belonging to the methanol series. In order to understand better the influence of H-bonds and hydrophobic interaction we compare their dependences with those for argon and hydrogen sulphide. It is taken into account that noted above thermodynamic properties are mainly determined by the averaged interparticle potentials, having the argon-like form. As a result they lead to the similarity of their specific volumes and thermal expansion coefficients practically for all their liquid states. Corrections caused by H-bonds and hydrophobic interactions do not exceed (4 ÷ 5)%. Only near the terminate points – triple and critical ones – the influence of H-bonds becomes determinative. It had been shown that the thermal expansion coefficient for water practically linearly diminishes for T → Ttr, near T ≈ 40C it becomes equal to zero and takes negative values for Ttr < T < 40C. As a result at the temperature T ≈ 40C the specific volume of water takes minimal value. It is also surprising that the thermal expansion coefficient for ethanol takes the minimal value at T ≈ − 40C.