Point and Enthalpy of Fusion

Melting points are listed for a large number of substances in data banks and handbooks. Their estimation is hardly possible, as they are influenced by the crystal structure, enthalpy of fusion, which represents the molecular interactions. 

The case is similar for the enthalpy of fusion. To a large extent, it depends on the structure of the crystal that is formed. In principle, the Clausius-Clapeyron equation can be applied however, the information about the pressure dependence of the melting point is usually not available. The so-called Walden rule [13] gives at least an estimation for aromatic compounds like benzene or naphthalene  

As the fusion process is accompanied by with a change in volume, the melting point is a function of pressure. Very high pressures can change the melting point significantly. Analogously to Eq. (2.86), the Clausius-Clapeyron equation can be applied  

Using Eq. (3.18), only trends can be predicted. The necessary input information about Ahm and Av with respect to temperature is usually missing. If data are available, the Simon-Glatzel equation [14] 

In a television broadcast [18] it was reported that at the bottom of the Mariana Trench, the deepest part of the world s oceans with a depth of 11000 m, the temperature is —2 which is below the well-known melting point of 0°C. Check whether this is plausible or not. The differences in the properties between pure water and sea water shall be neglected. For the liquid density of water, = 1000 kg/m shall be used. The pressure is 

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The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

Table 2.2 Enthalpies and temperatures of fusion and vaporization. Normal melting and boiling points and enthalpies of fusion and vaporization are tabulated by type of...

Rordorf, B.F. Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins and fifty-five dibenzofurans by a vapor pressure correlation method. Chemosphere, 18(l-6) 783-788,1989. Rosen, J.D. and Carey, W.F. Preparation of the photoisomers of aldrin and dieldrin. 7 Agric. Food Chem., 16(3) 536-537,1968. Rosen, J.D. and Strusz, R.F. Photolysis of 3-(p-bromophenyl)-l-methoxy-l-methylurea, 7 Agric. Food Chem., 16(4) 568-573, 1968. 

To be useful from a CALPHAD point of view, it is mandatory to have a characterisation of the liquid phase, and the insistence on working totally from FP has to be relaxed. The simplest solution is to add data for the melting points and enthalpies of fusion for the elements from conventional CALPHAD sources. As for heat of mixing for the liquid phase, one approximation is to assume it will follow a suitably weighted behaviour of the f.c.c. and b.c.c. phases. This kind of treatment... 

The choline salts of naproxen and tolmetin yielded marked solubility enhancements, even over that of the sodium salts. The aqueous solubility of the choline salt of naproxen was 6700 times the solubility of naproxen and almost twice that of naproxen sodium. The choline salt of tolmetin was almost 8000 times as soluble as the parent drug and almost 5 times as soluble as its sodium salt (Murti, 1993) (Cheenu dissertation, our unpublished results). Table 15.2 shows that the melting points and enthalpies of fusion are both affected by the formation of the choline salt, and in fact, the choline salt proved to be more thermally stable. 

Rordorf, B.F. 1989. Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins and fifty-five dibenzofurans by a vapor pressure correlation method. Chemosphere 18 783-88. 

TABLE 16.8 Melting Points and Enthalpies of Fusion for Several Representative Solids... 

Melting point and enthalpy of fusion data have been reported by several investigators. These results are summarized below ... 

Equation (1.6-7) shows the impottance of melting point and enthalpy of fusion. When other effects are equal, rhe ideal solubility declines as the distance between system teraparatute and melting temperature... 

Rand [1975RAN] and Glushko et al. [1982GLU/GUR] also assessed the melting point and enthalpy of fusion of thorium, selecting Tfus(Th, P) = (2023 + 10) K from eight studies and (Th, p, 2023 K) = (13.8 + 0.1) kJ-mol from Levinson... 

Ionic solids such as NaCI and NaF have very high melting points and enthalpies of fusion because of the strong ionic forces in these soiids. At the other extreme is Ojis), a moiecuiar soiid containing nonpoiar moiecuies with weak intermoiecuiar forces. (See Tabie 10.9.)... 

Thus the depression of the freezing point, A 7), of a liquid (molar mass. Mm, melting point, and enthalpy of fusion, AfUsTf" at 1 bar pressure) caused by addition of Wsoiute can be calculated using equation (51.37). 

Root mean squared error (RMSE) and squared correlation coefficient (/P) are shown for the COSMOquick approach using multiple reference solvents (multiple reference) and using a free energy of fusion estimate via the melting point and enthalpy of fusion quantitative structure-property relationship (QSPR) models. 

P8.7 Calculate the SLE behavior of the system p-toluidine-phenol with 1 1 compound formation assuming ideal behavior, where the melting point and enthalpy of fusion of the 1 1 compound should be adjusted to get a reliable description of the SLE behavior. Published data can be downloaded from the textbook page on www.ddbst.com. 

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