Enthalpies of fusion, data

What can be said about the thermochemistry of methylated cyclic ketones in any phase other than liquid In that we would have discussed gas-phase species if the data were available, what we are really asking is what can be said about the species of interest as solids , Let us generalize this to see what can be said about the thermochemistry of cyclic ketones as solids. In that the cyclic ketones in the previous section were all formally quite strain-free derivatives of cyclopentanone or cyclohexanone, let us now consider only such species and their cycloalkane analogs. There are no enthalpy-of-fusion data available for cyclopentanone. For cyclohexanone, the temperature-uncorrected fusion enthalpy is about 1.3 kJmol-1—we arbitrarily ignore in this discussion enthalpies of any crystal - different crystal phase enthalpy. The same treatment for cyclohexane discloses the fusion enthalpy of 2.7 kJmol-1. Accordingly, the earlier reported value of 638(6) = 104.4 for the gas phase is sequentially modified to ca 115 kJ mol-1 for the liquid and to 113 kJmol-1 for the solid. For 2-norbomanone, adamantanone and diamantanone (39a, 42 and 43), the gas-phase differences of 115.7 6.8, 96.0 5.1 and 90.6 3.2 become for the solids 124.4 6.8, 116.9 4.5 and 97.8 3.1 kJmol-1. Very roughly, 639( ) is some 10 kJmol-1 more positive for solids than for gases and 639(8) is about 113 kJmol-1 for all of the solids discussed here. 

Values in parentheses were derived from A//f (enthalpy of fusion) data obtained by mass spectroscopy and probably have some inherent error. 

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

The available fusion temperature and enthalpy of fusion data are summarized in the table below, and = 20.92 t 6.3 kJ mol ... 

Another way to estimate the subcooled liquid fugacity f - below the melting point is to use heat (enthalpy) of fusion data and, if available, the heat capacity data for both... 

Enthalpy of fusion data are generally taken from Domalski, E. S. Hearing, E. D. J. Phys. Chem. Ref. Data 1996,25,1 without any attempt to correct them from the value measured at the melting... 

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. 

He placed two 150.-g samples of water at 0.00°C (one ice and one liquid) in a room kept at a constant temperature of 5.00°C. He then observed how long it took for each sample to warm to its final temperature. The liquid sample reached 5.00°C after 30.0 min. However, the ice took 10.5 h to reach 5.00°C. He concluded that the difference in time that the two samples required to reach the same final temperature represented the difference in heat required to raise the temperatures of the samples. Use Black s data to calculate the enthalpy of fusion of ice in kj-mol-1. Use the known heat capacity of liquid water. 

The differential scanning calorimetry (DSC) thermogram of niclosamide was obtained using a General V4 IC DuPont 2100. The data points represented by the curve shown in Fig. 2 were collected from 200 to 400°C using a heating rate of 5°C/ min. It was found that the compound melted at 231.66°C with an enthalpy of fusion equal to 69.31 J/g. 

Unless otherwise said, our preferred sources for enthalpies of formation of hydrocarbons are Reference 8 by Roth and his coworkers, and J. B. Pedley, R. D. Naylor and S. P. Kirby, Thermochemical Data of Organic Compounds (2nd ed.), Chapman Hall, New York, 1986. In this chapter these two sources will be referred to as Roth and Pedley , respectively, with due apologies to their coworkers. We will likewise also occasionally take enthalpies of fusion from either E. S. Domalski, W. H. Evans and E. D. Hearing, Heat Capacities and Entropies of Organic Compounds in the Condensed Phase , J. Phys. Chem Ref. Data, 13, 1984, Supplement 1, or E. S. Domalski and E. D. Hearing, J. Phys. Chem Ref. Data, 19, 881 (1990), and refer to either work as Domalski . 

The enthalpy A W((lcUi is the energy required to melt 1 mol of material at constant pressure. We need to be careful when obtaining data from tables, because many books cite the enthalpy of fusion, which is the energy released during the opposite process of solidification. We do not need to worry, though, because we know from Hess s law that AH elt) = — A//( lsion). The molar enthalpy of melting water is +6.0 kJmol-1. 

Cimetidine is known to crystallize in 5 polymorphic forms and 3 hydrated forms [11]. Solubility data is presented in this reference for Forms A, B and C. Form E was not known at the start of the study in reference [11] and Form D could not be crystallized, suggesting that it is less stable than the other forms. This is confirmed by melting point data which indicates the order of thermodynamic stability close to the melting temperature isEmelting point data for the evaluated forms are presented in Table 3. Form A is the commercially available Form and the desired product for this case study. 

First a database of solute-solvent properties are created in SoluCalc. The database needs the melting point, the enthalpy of fusion and the Hildebrand solubility parameter of the solute (Cimetidine) and the solvents for which solubility data is available. Using the available data, SoluCalc first prepares a list of the most sensitive group interactions and fits sequentially, the solubility data for the minimum set of group interaction parameters that best represent the total data set. For a small set of solvents, the fitted values from SoluCalc are shown in Table 9. It can be noted that while the correlation is very good, the local model is more like a UNIQUAC model than a group contribution model... 

Unless indicated to the contrary, all measured enthalpies of fusion are taken from die compendia by Domalski and coworkers3 and by W. E. Acree, Jr., Thermochim. Acta, 189, 37 (1991) 219, 97 (1993) and a still unpublished supplement (personal communication). We thank Dr William Acree for providing us with his unpublished data. 

Applying Concepts When ice is added to water at room temperature, the water provides the energy for two processes. The first process is the melting of the ice. The energy required to melt ice is the enthalpy of fusion (AHfus). The second process is raising the temperature of the melted ice from its initial temperature of 0.0°C to the final temperature of the liquid water. In this experiment, you will collect data to calculate the enthalpy of fusion for ice. 

The value of Afus,c may be obtained by extrapolating Af s to the density of the eompletely crystalline polymer, whieh in turn may be obtained from x-ray diffraction data. The speeifie enthalpies of fusion are temperature-dependent. 

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... 

Troncoso, J. et al.. Thermodynamic properties of imidazolium-based ionic liquids densities, heat capacities, and enthalpies of fusion of [bmim][RF5] and [bmim][NTf2], /. Chem. Eng. Data, 51,1856, 2006. 

Dibenzofuran is a solid at ambient temperatures. Hence, the enthalpy of solution (AwHj) is given by the sum of the enthalpy of fusion (A H,) and the excess enthalpy in aqueous solution (Hfi,) (Fig. 5.1 and Eq. 5-25). In a paper by Shiu et al. (1997) you find aqueous solubility data expressed in g m for dibenzofuran at various temperatures (see margin). For simplicity, assume that Vw is temperature independent. 

Finally, we note that it will occasionally be necessary to use data for a species as liquid when the compound is normally a solid, or as a solid when it is normally a liquid. These two phases are interrelated by the enthalpy of fusion, equation 3. 

We have enthalpy-of-formation data for both 1,1- and (Z)-l,2-bis(p-tolyl)ethylene as solids. What is lacking are the corresponding data for the diphenylethylenes, or equally useful, the enthalpies of fusion of these two hydrocarbons. 

The magnitudes of the solubility of forms I and II of this drug varied signiLcantly in water, decyl alcohol, and dodecyl alcohol. However, their data showed that the solubility ratio was independent of solvent, but dependent on temperature. Figure 19.3 shows the data for these polymorphs in water The difference in slopes (indicating a difference in enthalpies of fusion) for the two polymorphs can be used to calculate a transition temperature, where both forms have the same physical stability The identity of the metastable form and the degree of solubility enhancement both depend on the temperature chosen for comparison. 

In spite of the wealth of information available on the preparative and structural aspects of the lanthanide chlorides (1-3), experimental thermodynamic, and, in particular, high-temperature vaporization data are singularly lacking. The comprehensive estimates of the enthalpies of fusion, vaporization, heat capacities and other thermal functions for the lanthanide chlorides by Brewer et ah (4, 5) appear internally consistent, but the relatively few experimental measurements (6-/2) do not permit confirmation of the estimates due to the narrow temperature ranges of study. Additionally, the absence of accurate molecular data for the gaseous species has hampered third-law treatment of the limited experimental vapor pressure data available. The one reported study (12) of the vaporization of EuC12 effected by a boiling-point method lacks accuracy for these reasons. 

Fig. 1 Composition dependence of the thermal transition parameters, Tg, Tm, and AFZf, estimated by DSC for CA-g-PLA samples (acetyl DS = 2.15). Data for Tm (melting temperature) and AHf (enthalpy of fusion) were obtained in the first run, while Tg was evaluated in the second. (Quoted from [23] with an adequate modification)...

The DSC thermogram of spironolactone was obtained using a Du Pont TA-9900 thermal analyzer system, interfaced to the Du Pont data collection system. The thermogram shown in Figure 3 was collected over a range of 50 to 250°C, using a heating rate of 10°C/minute. It was found that the compound melted at 210.5°C, with an enthalpy of fusion equal to 43.40 J/g. 

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