Volume change, on melting

Bockris and Richards experimental value of the free volume for KCI (V = 0.68 cm mol" ) agrees well with that of Woodcock and Singer. The volume change on melting obtained experimentally, however, is 8.2 cm mor )which is only 3% less than the entirely acceptable calculated value obtained by Woodcock and Singer s Monte Carlo simulation. Their actual model for liquid KCI is shown in Fig. 5.14 and appears to contain hole volume corresponding to modelistic concepts which feature this property (Section 5.5.1). 

Now it is known that this is not true for all substances the examples of cadmium, sodium chloride, and potassium chloride were cited in Section III. A, where the lack of wetting behavior led to an experimental method for measuring ffj,. If, however, this result is assumed to hold true, then the calculation reduces to a calculation of and a separate calculation or measurement of ff( . Skapski then estimates the difference in energy of the bonds broken to form the solid-vapor and liquid-vapor interfaces from the enthalpy of fusion of the bulk solid and the volume change on melting, and adds to it a small estimated contribution from the entropy change in the outer layer of the liquid and of the solid. The result is... 

The solubility parameter and liquid molar volume for n-bexane are given in Table 9.6-1 as A = 7.3 and Y2 = 132 cc/mol, respectively. Since the liquid molar volume of naphthalene given in the data is for a temperature 80° C higher than the temperature of interest, and the volume change on melting of naphthalene is small, the molar volume of liquid naphthalene below its melting temperature will be taken to be that of the solid that is. 

Table 10-4. Enthalpies of fusion, AHm, entropies of fusion, ASm, and specific volume changes on melting, Avm, of polymers. 

The enthalpy of melting can be readily determined by non-calorimetric methods. One method involves the determination of the cryoscopic constant of the solvent from the temperature depression observed by the addition of a non-associating solute. The second method, using the Clapeyron equation, involves measuring the volume change on melting for the solvent and the pressure dependence of the melting temperature of the solvent. ... 

It has already been pointed out that the volume changes on melting, usually increasing (see Figure 6.2). This phenomenon may be used to study the kinetics of crystallization. Figure 6.25 (69) illustrates the isothermal crystallization of poly(ethylene oxide) as determined dilatometrically. From Table 6.1 the melting temperature of poly(ethylene oxide) is 66°C, where the rate of crystallization is zero. The rate of crystallization increases as the temperature is decreased. This follows from the fact that the driving force increases as the sample is supercooled. 

Table 1.7 Volume changes on melting for organic compounds [22] ...

Rasmussen, 0.3., Surface Tension, Density and Volume Change on Melting... 

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