Free energy of vaporization

The Eq for the free energy of vaporization of nitric acid for the temp range 275-305°K has been obtained from vapor pressure measurements (Ref 30)... 

The vapor pressure of chlorine dioxide, Cl02, is 155 Torr at —22.75°C and 485 Torr at ().()0°C. Calculate (a) the standard enthalpy of vaporization (b) the standard entropy of vaporization (c) the standard Gibbs free energy of vaporization (d) the normal boiling point of C102. 

Molecular weight and Gibbs free energy of vaporization AGV (Burkhard et al. 1985a) ... 

Enthalpy and Entropy Contributions to the Free Energy of Vaporization... 

By denoting G, as AvapG the free energy of vaporization of the liquid compound, and by omitting to write down every time that we have to divide pL by p° (which is commonly 1 bar), we get ... 

Now we can see how a chemical s structure causes it to have a particular vapor pressure. This is possible because, as a first approximation, the free energy of vaporization, A G, mostly differs from compound to compound due to differences in those substances enthalpies of vaporization, Avap//,-. These enthalpies reflect the sum of intermolecular attractions that act to hold those liquid molecules together. Thus, we can expect that substances that exhibit high vapor pressures have structures that do not enable the molecules to have strong intermolecular attractions. Conversely, molecules with low vapor pressures must have structures that cause the molecules to be substantially attracted to one another. 

Unless stated otherwise, the values have been taken from the compilations by K. K. Kelley on Heats of Fusion of Inorganic Compounds, U.S. Bur. Mines Bull. 393 (1936), and The Free Energies of Vaporization and Vapor Pressures of Inorganic Siibstances, U.S. Bur. Mines Bull. 383 (1935). 

KEL] Kelley, K. K., Contributions to the data on theoretical metallurgy. IIL Free energy of vaporization and vapour pressure of inorganic substances, Bull. - U. S., Bur. Mines, 383, (1935), Cited on page 173. 

Many procedures have been developed to predict vapor pressure, and the predictive error of eleven different methods have been evaluated using a series of PCBs. A number of approaches use a set of known vapor pressures to develop a correlation with molecular properties that can be used for predictions of unknowns. For example, the free energy of vaporization has been correlated with molecular surface area to predict vapor pressures of PCB congeners. More direct approaches are based on the Clausius-Clapeyron equation, and vapor pressures can be predicted quite effectively for some series of compounds using only boiling points along with melting points for compounds that are sohds at ambient temperatures. 

Table 4.14 contains AG values calculated in two ways, together with the experimental standard AG values for dissolution of sodium chloride, determined in various solvents. As regards the calculated values, the first (I) was obtained from the above equation, whereas in the calculation of the second (II) the term proportional to the standard free energy of vaporization, describing the energy of cavity formation in the solvent, was replaced with a constant C. 

AvapGfi Partial molar free energies of vaporization... 

The stoichiometric standard variation of the Gibbs free energy of vaporization of component i in an infinitely dilute solution at average... 

The stoichiometric variations of standard Gibbs free energies of vaporization of single solutes A G result from fugacities and molar volumes [26] ... 

K. K. Kelley, Contributions to the Data on Theoretical Metallurgy - III - The Free Energies of Vaporization and Vapour Pressures of Inorganic Substances , U.S. Bureau of Mines, Bulletin 383, 1935. 

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