Reanalysis of the Much Referenced Ethanol-trichloromethane Mixture Vapor Pressure Data: A Discussion of the Principal Association Species Present

Abstract

The Scatchard (S) and Raymond (R) 1938 data on the vapor pressure above ethanol (1)-trichloromethane (2) mixtures at the temperatures of 35, 45 and 55° C are still being used today in discussions of the thermodynamic properties and association species present in 1-2 mixtures. Here a detailed reanalysis of the originally published SR data has been carried out using the model free Redlich-Kister excess chemical potential approach as applied by Barker. These results show how small temperature variations drastically affect mixture vapor pressure measurements. A number of weaknesses in SR's original analysis of their data and significant discrepancies between R's thesis results and those in the published SR paper have been uncovered. These discrepancies would impact the conclusions of anyone using SR's results. From the present reanalysis more accurate temperatures dependent Gibbs excess energies, excess entropies, excess enthalpies and activity coefficients have been calculated that could not been obtained from SR data analysis scheme. Based on available experimental and theoretical studies of the 1-2 system it is argued that the major association species should be the cyclic 111 trimer and that the dimer 22 should be considered. This is counter to a current model for this system.

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