Reduced enthalpy increment

Enthalpy increment measurements to derive the high-temperature heat capacity have been reported for all lanthanide trifluorides except PmF3, as summarised in table 7. The results of the various authors are compared using the reduced enthalpy increment function ... 

Fig. 14. The reduced enthalpy increment of LaF3 (in J-K 1-mol 1) o, Henderson (1970) Lyon et al. (1978) , value at 298.15 K derived from the low-temperature heat capacity measurements of Lyon et al. (1978).

Fig. 16. The reduced enthalpy increment of CidC 13 (in J K fmor1) , Sommers and Westrum Jr. (1977) o,...

Fig. 17. The reduced enthalpy increment of LaCl3 (in J-K 1 -mol 1 ) , Sommers and Westrum Jr. (1976) o, Dworkin and Bredig (1963a) broken line (1), Gaune-Escard et al. (1996) broken line (2), Reuter and Seifert (1994).

The heat capacity values calculated using this equation join smoothly the heat capacity data of [65WES] at temperatures below 50 K. A comparison between the heat capacity values calculated using Eq.(V.25) and the experimental data (heat capacity and reduced enthalpy increments) are illustrated in Figure V-20. 

Figure V-29 Comparison of calculated and experimental values of the reduced enthalpy increment of ZrSiO cr) between 50 and 1823 K. The data are taken from [41KEL] (o), [50COU/K1N] (A) and [61V1C/DOU] ( ). Only the data of [41KEL] and [61VIC/DOU] were used for derivation of the calculated data (line).

Comparison of calculated and experimental values of the reduced enthalpy increment of ZrSi04(cr) between 50 and 1823 K.218... 

Figure 7-6. Shomate plot of the reduced enthalpy increment of Ce02 the symbols represent the experimental values the solid line the recommended equation the symbol the value of the heat capacity at T = 298.15 K from the low-temperature measurements.

Because of the drift in the decomposition pressure data, it is pertinent to assess the uncertainty in the functions. The greatest potential source for error is in the values above room temperature where the increment of entropy is about 20 cal K mol" between 298.15 and 700 K. Unfortunately, no evaluation of the unpublished enthalpies is possible, but an increase of 10% in the entropy Increment would reduce the drift to a tolerable level. 

Pulse thermal analysis (PulseTA ) [1] eliminates, or at least reduces, the difficulties mentioned above. PulseTA is based on the injection of a specific amount of the gases or liquids into the inert carrier gas stream and subsequent monitoring of changes in the mass, enthalpy and gas composition, resulting from the incremental reaction extent. Because a known amount of the selected gas, which can be used for calibration, is injected into the system, the method is also suitable for quantification of the evolved gas by mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTTR). In contrast to conventional TA and all its modifications, the reaction is controlled not only by the temperature, but also by a distinct change in the composition of the reactive atmosphere. 

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