Fusion, entropy tables

Table 4. Total Entropies of Fusion, Entropies of Fusion at Constant Volume and Volume Changes on Fusion ...

Let us first consider the ice-water equilibrium. For the ice water transition, AH is the molar heat of fusion (see Table 11.8), and T is the melting point. The entropy change is therefore... 

Self-Tfst 7.8A Calculate the standard entropy of fusion of mercury at its freezing point (see Table 6.3). 

C14-0050. Table lists molar enthalpies of fusion of several substances. Calculate the molar entropy of fusion at its normal melting point for each of the following (a) argon (b) methane (c) ethanol and (d) mercury. 

In Table XXXV are given the heats and entropies of fusion (AaSu = I Hu/T where is in °K) for various polymers. The melting... 

Table XXXV.—Heats and Entropies of Fusion of Polymers...

Table 4 Heats and entropies of fusion for crystalline stearoylserine methyl ester. , i ...

Table 6.1. Correlation between the entropy of fusion (extrapolated to Tm = 0) and the Lindemaim constant (C/,) for various crystal structures (from Achar and Miodownik 1974)...

Other features of this behavior are illustrated concretely using the Hg-Te system. The calculations were made using values for the thermodynamic properties that are slightly different than those shown in Table VII and used in the calculations described in the main text. Thus the calculations are not quite correct for Hg-Te but are still valid for illustrative purposes. The enthalpy of fusion is taken as 8,680 cal/mol and the enthalpy and entropy of formation of HgTe(s) at 943. as -13,933 cal/mol and —9.538 cal/°K mol, respectively. After applying the constraints of Eqs. (109)—(111) and setting / 13 = / 14 = / 34 = 0, the independent model parameters are z, SlR, and SlA. The former... 

Hence, now we are left with the problem of estimating the entropy of fusion at the melting point. Unfortunately, A A, (Pm) (Table 4.5) is much more variable than AvapS( (Tb) (Table 4.2). This might be expected since AfusSt (Tm ) is equal to SiL (Tm) - SiS (Tm) and both of these entropies can vary differently with compound structure. One reason is that molecular symmetry is an important determinant of the properties of a solid substance in contrast to a liquid, where the orientation of a molecule is not that important (Dannenfelser et al., 1993). Nevertheless, as demonstrated by Myrdal and Yalkowski (1997), a reasonable estimate of A S) (Tm) can be obtained by the empirical relationship (Table 4.5) ... 

Table 4.5 Comparison of Experimental and Predicted (Eq. 4-39) Entropies of Fusion at the Normal Melting Point0...

Table II gives heats and entropies of fusion for selected aromatic polycondensates.

If we want to calculate the entropy of a liquid, a gas, or a solid phase other than the most stable phase at T =0, we have to add in the entropy of all phase transitions between T = 0 and the temperature of interest (Fig. 7.11). Those entropies of transition are calculated from Eq. 5 or 6. For instance, if we wanted the entropy of water at 25°C, we would measure the heat capacity of ice from T = 0 (or as close to it as we can get), up to T = 273.15 K, determine the entropy of fusion at that temperature from the enthalpy of fusion, then measure the heat capacity of liquid water from T = 273.15 K up to T = 298.15 K. Table 7.3 gives selected values of the standard molar entropy, 5m°, the molar entropy of the pure substance at 1 bar. Note that all the values in the table refer to 298 K. They are all positive, which is consistent with all substances being more disordered at 298 K than at T = 0. 

The thermal data on possible condis crystals are collected in Table 8. Substantial entropy gains are observed at the disordering transition, but variations are large, depending on the amount of conformational mobility gained. When compared to the total entropy of fusion, the listed entropies of disordering vary from 30 %, for polytetrafluoroethylene, to close to 100% for the polyphosphazenes. 

The entropy of fusion in cal deg-1 g-1 is easily computed from the data of Table 3 by dividing the heats of fusion by the absolute temperature of the melting point. For theoretical reasons in many cases it is interesting to know the entropy of fusion at constant volume. Thus, the total measured entropy of fusion at constant pressure and composition, ASf, must be corrected for the gain in entropy due to the volume increase on fusion. The fusion process may be imagined as occurring at... 

The enthalpies of fusion that have been derived from the enthalpy increment equations for the solid and liquid phase are listed in table 13 and the derived entropies of fusion are plotted in fig. 29. It can be seen that the enthalpies and entropies of fusion for ErF3 to LuF3 are significantly lower than those of the other lanthanide trifluorides. Because these four compounds... 

Heat capacity is (9.1 + 2.9 x 10 3 T(K)) cal mol 1 K 1 between 298 and 1273 K, while entropy is 10.4 cal mol 1 K 1 at 298.15 K [30], More recent heat capacity data between 153 and 293 K are quoted in TABLE 3, Datareview A1.4 of this volume. There is a 7.5% discrepancy between the two sets of data at room temperature. The inferred Debye temperature is 660 K [29], Enthalpies, entropies and Gibbs functions of fusion and formation are given in TABLE 4. Thermochemical data should also be regarded with circumspection in particular the early value of AH°f = -5 kcal mol 1 [1] is often quoted but should now be discarded in favour of more recent results [24,31] found to lie close to those for the other nitrides. 

The Entropy of Melting.—When wc look at the entropies of melting, in Table XVI-1, we see that there is a certain amount of regularity in the table. For most of the metals, the entropy of fusion is... 

The value (3.6), while appreciable compared with the values of Table XVI-1, which are of the order of magnitude of two or more calorics per degree, is definitely less, so much less that it cannot possibly account for the whole entropy of fusion. Let us see what value of a we should have to take to get the whole entropy of fusion from this term. If we set a — 1, for instance, we have... 

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