Vaporization from Watson correlation

Estimates of the latent heat of vaporization of a pure Hquid at any temperature from a known value at a single temperature are possible by several methods. The known value may be experimental, or it may be estimated by equation 16. Of the methods proposed, the Watson correlation (1), which is both simple and reHable, has found the greatest acceptance ... 

A prerequisite for applying estimation techniques is the knowledge of the compound s boiling point (r, ) and for solids also of the melting point The methods described by Grain (1990), Lyman (1985) and Altschuh, Briiggemann and Karcher (1993) are of general applicability and they are not restricted to particular chemical classes. In Table 4.4, model 1 is derived from the Antoine equation, which describes the temperature dependence of vapour pressure model 2 is based on the Watson correlation, which describes the temperature dependence of the heat of vaporization model 3 constitutes an extension of 2. These three models additionally use a class-specific constant (Kp) as input, which is assumed to describe the polarity of the compounds (Table 4.5). 

A procedure for calculating the latent heat of vaporization at one temperature from a known value at any other temperature was presented in Section 8.4a. The technique outlined is rigorous but time-consuming, and it requires heat capacity data that might not be available for the substance of interest. A useful approximation for estimating AHy at T2 from a known value at T is Watson s correlation ... 

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 Thermoctynamio Data Applied to the Vapor-Pressure Curve of Argon, Nitrogen, and Water, J.T.R. Watson (trans. and ed.), lUPAC Thermodynamic Tables Project Centre, London, 1977 Ambrose, D.,/. Chem. Thermodyn., 18 (1986) 45 Ambrose, D., and N. B. Ghiassee,/. Chem. Thermodyn., 19 (1987) 903, 911]... 

Results from the data compilation of Yaws and co-workers (44,52) were selected. Data for heat of vaporization were correlated using the Watson equation ... 

The data compilation of Yaws and co-workers (52) was selected for heat of vaporization for temperatures ranging from melting point to critical point. The Watson equation, Equation (1-2), was used for correlation of the data as a function of temperature. Reliability of results is good with errors of about 1-5% or less. 

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