On the Analyses of Mixture Vapor Pressure Data: The Hydrogen Peroxide/Water System and Its Excess Thermodynamic Functions

• Published in: Chemistry : a European journal Vol. 10; no. 24; pp. 6540 - 6557
• Main Authors: Manatt, Stanley L., Manatt, Margaret R. R.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 17.12.2004; WILEY‐VCH Verlag
• Subjects: hydrogen peroxide; liquid mixture vapor pressures; phase equilibria; thermodynamics; water chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200400104

Reported here are some aspects of the analysis of mixture vapor pressure data using the model‐free Redlich–Kister approach that have heretofore not been recognized. These are that the pure vapor pressure of one or more components and the average temperature of the complex apparatuses used in such studies can be obtained from the mixture vapor pressures. The findings reported here raise questions regarding current and past approaches for analyses of mixture vapor pressure data. As a test case for this analysis approach the H2O2–H2O mixture vapor pressure measurements reported by Scatchard, Kavanagh, and Tickner (G. Scatchard, G. M. Kavanagh, L. B. Ticknor, J. Am. Chem. Soc. 1952, 74, 3715–3720; G. M. Kavanagh, PhD. Thesis, Massachusetts Institute of Technology (USA), 1949) have been used; there is significant recent interest in this system. It was found that the original data is fit far better with a four‐parameter Redlich–Kister excess energy expansion with inclusion of the pure hydrogen peroxide vapor pressure and the temperature as parameters. Comparisons of the present results with the previous analyses of this suite of data exhibit significant deviations. A precedent for consideration of iteration of temperature exists from the little‐known work of Uchida, Ogawa, and Yamaguchi (S. Uchida, S. Ogawa, M. Yamaguchi, Japan Sci. Eng. Sci. 1950, 1, 41–49) who observed significant variations of temperature from place to place within a carefully insulated apparatus of the type traditionally used in mixture vapor pressure measurements. For hydrogen peroxide, new critical constants and vapor pressure–temperature equations needed in the analysis approach described above have been derived. Also temperature functions for the four Redlich–Kister parameters were derived, that allowed calculations of the excess Gibbs energy, excess entropy, and excess enthalpy whose values at various temperatures indicate the complexity of H2O2–H2O mixtures not evident in the original analyses of this suite of experimental results. Iterative Redlich–Kister analyses of mixture vapor pressure (MVP) data yield significantly less error with the experimental data if the temperature and pure vapor pressures are also parameters. These results suggest a vast amount of literature MVP data should be reanalyzed. Results on the H2O2–H2O system demonstrate this approach; solution complexities not evident in previous works (upper three curves, left figure) are revealed (lower two curves, left figure).