Enthalpy, Entropy and Heat Capacity

Reported molar heat capacity data are summarized in Table S.deNovion [15] and deNovion, Costa [16] fitted their low temperature data over the temperature range 1.3 to 10 K to the empirical equation C, Cp=YT + aT  

From the temperature variation of the X-ray powder diffraction peak profiles of ThN, Aronson, Ingraham [28] calculate the characteristic Debye temperatures 0d = 234 15 K on the basis of a heavy-mass model and 0q = 317 K for an average-mass model. They give more credence to the former value in view of the large difference in masses between Th and N atoms and they claim that it agrees better with published entropy data. 

High-temperature heat capacity data for ThN are summarized in rows 6 to 9 of Table 5. The data estimated by Rand [8] and given by the equation 

Based on their measurements of the low temperature heat capacities, the standard absolute entropy of ThN is reported as SJae=13.38 0.24 cal-mor K by Danan etal. [23] and Danan [22] and as 13.7 0.2 cal-mor -K by Dell, Martin [24]. Following the precedent set by Rand [8], the latter value is adopted for consistency with data on Th3N4. 

The following data are useful for converting reference states from 298.15 to 0 K [22, 23]  

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Coefficients for equations which express the dependence of heat capacity, enthalpy, and entropy on temperature, in the range 150-6000 K have also been computed [801] for the purpose of obtaining equilibrium compositions and theoretical rocket performance of propellants the form of the equations are given below (the actual coefficients are too dated to be worth quoting) ... 

TAR/ZHD] Tarasov, V. V., Zhdanov, V. M., Mal tsev, A. K., Low-temperature heat capacity, enthalpy, and entropy of germanium disulfide and germanium diselenide, Russ. J. Phys. Chem., 42, (1968), 685-687. Cited on page 210. 

Some sample properties may be obvious to the analyst, such as colour, shape and dimensions or may be measured easily, such as mass, density and mechanical strength. There are also properties which depend on the bonding, molecular structure and nature of the material. These include the thermodynamic properties such as heat capacity, enthalpy and entropy and also the structural and molecular properties which determine the X-ray diffraction and spectrometric behaviour. 

The solubilities of the scale-forming salts barium and strontium sulphates in aqueous solutions of sodium chloride have been reviewed by Raju and Atkinson (1988, 1989). Equations were proposed for the prediction of specific heat capacity, enthalpy and entropy of dissolution, etc., for all the species in the solubility equilibrium, and the major thermodynamic quantities and equilibrium constraints expressed as a function of temperature. Activity coefficients were calculated for given temperatures and NaCl concentrations and a computer program was used to predict the solubility of BaS04 up to 300 °C and SrS04 up to 125 °C. 

Summary of Heat Capacity, Enthalpy, and Entropy Values... 

Statistical thermodynamics provides exact formulas for the calculation of the fundamental quantities of heat capacities, enthalpies and entropies, provided that certain assumptions are valid. Among these assumptions are ... 

In the remainder of this section we discuss the derivation of group values for heat capacities, enthalpies and entropies and provide several examples to illustrate their application. In Section V we will discuss refinements to this simple group additivity scheme. There, the aim is to see if, by a simple expansion beyond the four parameters required for group additivity, we can improve significantly upon its accuracy in predicting thermochemical properties. 

A limited number of low temperature heat capacity measurements have been described. The adiabatic calorimetric measurements of Westrum and Beale (1961) are the only data available for the trifluorides. Similar heat capacity measurements have recently been reported for the lighter lanthanide trichlorides (La-Gd) in the range 5-350 K (Sommers, 1976), and for EuBr3 in the range 5-340 K (Deline et al., 1975). Heat capacities, enthalpy and entropy increments... 

Data in [1.39] indicate that the temperature dependence of heat capacity, enthalpy, and entropy are somewhat steeper. The values of C , — // ) and S%... 

Evans DM, Hoare FE, Melia TP (1962) Heat capacity, enthalpy and entropy of citric acid monohydrate. Trans Faraday Soc 58 1511-1514... 

The inputs include the number of atoms in the molecule and values of heat capacity, enthalpy and entropy at given temperatures. The heat capacity limits are computed from the number of atoms assuming a nonlinear molecule unless a linear one is specified in the input namelist. An optimum (to 50 units) value of B is found by minimizing the standard deviation of the match to the input data. The polynomial coefficients are obtained from the heat capacity fit. Using these coefficients the constants of integration I and J are found by comparing computed to input values of enthalpy and entropy. 

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