Standard entropy change variation with temperature

At first, we observe that no data are provided about the molar heat capacities of the components or about their variations with temperature. Consequently, we assume that the standard enthalpies and entropies do not vary with temperature between two state changes. 

Bakeeva, Pashinkin, Bakeev, and Buketov [73BAK/PAS] measured the selenium dioxide pressure over gold selenite in the interval 489 to 599 K by the dew point method. The pressure was calculated from the dew point temperature by the relationship for the saturated vapour pressure in [69SON/NOV]. The data in the deposited VlNITl document (No. 4959-72) have been recalculated with the relationship selected by the review. The enthalpy and entropy changes obtained from the temperature variation of the equilibrium constant are A //° ((V.123), 544 K) = (576.8 13.0) kJ-mol and A,S° ((V.123), 544 K) = (899.4 + 24.0) J-K -mor. The uncertainties are entered here as twice the standard deviations from the least-squares calculation. 

More interesting for practical applications is the approach of Pompe et al. [22] where two GC thermodynamic parameters (standard-state changes of enthalpy, AH°, and of entropy, AS°) are estimated. Since these parameters can be used to describe the variation of retention with temperature (see Section 3.2.2), estimations of retention can be extended to other temperature conditions, including programmed temperature. 

Much has been written about the relative merits of standard free energies, enthalpies and entropies as fundamental properties to elucidate chemical processes (see, for example, Taft, 1956 Leffler and Grunwald, 1963 Hepler, 1963 Larsen and Hepler, 1969 Wells, 1968 Exner, 1964a, b Hammett, 1970 Bell, 1973). In our opinion this question can only be answered in terms of the use to which the data will be put. Since AG°, AH° and AS° at room temperature all contain kinetic energy (partition function) terms, none of these properties corresponds exactly to the potential energy. Physical organic chemists are not put off much by this fact since they are usually more concerned with how properties change in response to systematic variation of molecular structure or solvent than they arc in particular properties of individual compounds. 

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