Argon, thermodynamic data

In the dense phase the intermolecular potential consists mainly of a two-body term to which small three-body contributions should be added. This problem is poorly documented for molecular systems, and the classic example remains that of argon where an effective two-body Lennard-Jones potential accounts fairly well for the thermodynamic data simply as a result of cancellation of errors. For vibrational energy relaxation one is not directly concerned with the whole intermolecular potential, but rather by its vibrationally dependent part. As mentioned earlier, three-body effects are not usually observable and may be masked by inadequate knowledge of the true potential. Nevertheless one can expect some simply observable solvent effects describable by changes of either the intermolecular or the vibrational potentials. 

Data from the triple point to the critical point can be correlated with either a modified form of the Wagner equation [Wagner, W, "A New Correlation Method for Thermodynamic Data Applied to the Vapor-Pressure Curve of Argon, Nitrogen, and Water, j.T.R. Watson (trans. and ed.), IUPAC Thermodynamic Tables Project Centre, London, 1977 Ambrose, D., J. Chem. Thermodyn., 18 (1986) 45 Ambrose, D., and N. B. Ghiassee,. Chem. Thermodyn., 19 (1987) 903, 911]... 

With these purely thermodynamic questions disposed of, one can hope that the future will bring a number of really complete experimental studies (both isotherm and calorimetric measurements, including heats of immersion and heat capacities in some cases) of the simplest possible systems—for example, argon or krypton adsorbed on nonpolar, non-porous adsorbents. Work along these lines is already in progress in the laboratories of J. A. Morrison and G. Jura. Aside from intrinsic interest, a backlog of detailed thermodynamic data of this type should prove invaluable for future theoretical attempts to understand the nature of adsorbed films. 

The thermodynamic data of carbon dioxide and other fluids are compiled in International Thermodynamic Tables of the Fluid State published by the International Union of Pure and Applied Chemistry (lUPAC) [28] in the form of tables and equations of state. Thermodynamic data and equations of state are also provided by Journal of Physical and Chemical Reference Data for argon [29], nitrogen [29], oxygen [29], carbon dioxide [30], methane [31], ethane [31], propane [31], butane [31, 32], isobutene [31, 32], ethylene [29] and methanol [33]. Fluid Phase Equilibria , Journal of Supercritical Fluids and Chemical Engineering Science are also good sources of thermodynamic and thermochemical data of SCFs. Data for phase diagrams. 

Din was the editor of a series of books designed to provide reliable thermodynamic data for industrially important gases. Temperature-entropy diagrams were chosen as the most generally useful graphical presentations and these are supplemented by tables of entropy, enthalpy, volume, heat capacity at constant pressure and at constant volume, and Joule-Thomson coefficients. Unfortunately, there is no consistency in the choice of units, although the thermochemical calorie is employed. The report on each substance (i.e. ammonia, carbon dioxide, carbon monoxide, air, argon, acetylene, ethylene, and propane) consists of a brief introduction, a survey of experimental data, a description of methods used for the thermodynamic calculations, and a set of tables. 

Table 16.1 Comparison of the calculated structure of liquid Argon with the experimental data obtained by X-ray diffraction in the same thermodynamic condition (T = 91.8 K and P = 1.8 atm)...

W have previously reported (3, 5) studies of the adsorption of argon at 77° and 90° K on muscovite mica which had been treated to replace the exchangeable surface potassium ions with other cations. The adsorption isotherms and thermodynamic functions evaluated from them showed significant differences among the various ion exchanged forms of mica. We have now obtained data for the adsorption of krypton on these substrates, and wish to discuss the differences in the behavior of the argon-mica and krypton-mica systems. 

Angus, S., and Armstrong, B., lUPAC Chemical Data Series No. 5, International Thermodynamic Tables of the Fluid State Argon, 1971, Butterworths, London, 1972. 

FIG. 2-5 Pressure-enthalpy diagram for dry air. Properties computed with the NIST REFPROP Database, Version 7.0 (Lemmon, E. W., McLinden, M. O., and Huber, M. L., 2002, NIST Standard Reference Database 23, NIST Reference Fluid Thermodynamic and Transport Properties—REFPROP, Version 7.0, Standard Reference Data Program, National Institute of Standards and Technology), based on the equation of state of Lemmon, E. W., Jacobsen, R. T., Penoncello, S. G., and Friend, D. G., Thermodynamic Properties of Air and Mixtures of Nitrogen, Argon, and Oxygen from 60 to 2000 K at Pressures to 2000 MPa, /, Phys. Chem. Ref. Data 29 331-385, 2000. 

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