EFFECT OF PRESSURE ON EXCESS THERMODYNAMIC CHARACTERISTICS OF WATER + FORMAMIDE MIXTURE

Abstract

Using the experimental data on the densities at atmospheric pressure and compressibility coefficients, k=(Vo-V)/Vo, of water + FA mixture the changes in the following thermodynamic parameters were calculated under the pressure increase up to 100 MPa within the temperature range from 288.15 to 323.15 K: excess molar Gibbs energy, ΔPo→PGmE, excess molar entropy ,ΔPo→PSmE, and excess molar entropy ΔPo→PHmE. It was established that ΔPo→PGmEvalues were negative over the whole concentration range and minima appeared on ΔPo→PGmE= f(x2) functions at x2≈0.33. The pressure growth up to 100 MPa resulted in ΔPo→PGmE absolute values increase within entire concentration and temperature intervals. The changes in entropy component, -(ΔPo→PTSmE), of ΔPo→PGmEvalues were almost canceled by the enthalpy component changes. Minimal values of ΔPo→PSmE corresponded to x2≈ 0.33, exactly at that composition 2Н2О-FA associate formed. The isobaric temperature lowering caused the structure ordering also at x2≈ 0.33. The pressure growth promoted the increasing in exothermicity of the mixing enthalpies, HmE, of water and formamide. The changes in HmE value under the mixture compression are indicative of the larger exothermal contribution from new H-bonds formation as compared with the endothermic contribution from the decreasing in the total amount of hydrogen bonds. The temperature lowering decreases ΔPo→PHmEvalues as well; maximal isotherms dispersion is observed at concentrations corresponding to maximal content of 2:1 or 1:1 associates of water and FA.