Standard entropy, of formation

Entropy of Formation The ideal gas standard entropy of formation (AS°298) of a chemical compound is the increment of entropy associated with the reaction of forming that compound in the ideal gas state from the constituent elements in their standard state definea as the existing phase at a temperature of 298.15 K and one atmosphere (101.325 kPa). Thus ... 

Standard enthalpies of formation, A / , and standard entropies of formation, at... 

The standard entropy of formation of an ion is related to the standard entropies of the species participating in the formation reaction ... 

Just as we can define a standard enthalpy of formation (AH°f) and a standard free energy of formation (AG°f), we can define an analogous standard entropy of formation (AS°f) as being the entropy change for formation of a substance in its standard state from its constituent elements in their standard states. Use the standard molar entropies given in Appendix B to calculate AS°f for the following substances ... 

If the elements are liquid in the standard state specified by the formation reaction, the Neumann-Kopp rule (115) suggests that ACp = 0. For the standard formation reaction in which Kn = 0 at the compound melting temperature, the standard entropy of formation can be obtained from the temperature derivative of AGf°[ij] or, often more accurately, from a combination of values of AGf°[ij, Tmij] and AHf°[ij, Tmij]. When Kn = 1 at TmiJ , the value of the natural standard entropy of formation, A Sf°[ij, Tmij], must be corrected as follows ... 

The calculations of standard thermodynamic properties discussed in the rest of this section are based on the assumption that the standard enthalpies of formation of species are independent of temperature in other words, the heat capacities of species are assumed to be zero. In the future when more is known about the molar heat capacities of species, more accurate calculations can be based on the assumption that the molar heat capacities are independent of temperature. When the heat capacities of species are equal to zero, the standard entropies of formation are also independent of temperature. Under these conditions the values of AfG at other temperatures in the neighborhood of 298.15 K can be calculated using... 

Equations 10.3-9 and 10.3-12 raise an issue about conventions for the hydrogen ion in thermodynamic tables. Since it is not possible to connect the standard thermodynamic properties of EI+ to those of molecular hydrogen, the convention is that AfG°(H + ) = 0 and Af//°(H + ) = 0 at each temperature. This indicates that the standard entropy of formation of a hydrogen ion AfS°(H+) should be taken as zero at each temperature, but, for historical reasons, the convention adopted in current thermodynamic tables is S°(H+) = 0 at each temperature. In principle, the value of S, (H + ) should be calculated from AfS EI4) for the formation reaction for H +. One way to write this reaction is... 

In the case of reactions, as opposed to processes, in order to calculate AS we can use standard absolute entropies or standard entropies of formation derived from thermochemical tables. 

Using standard entropy of formation data, A S Equation (11.9) applies. 

In the present study, the y values of the compounds were determined by measuring the Cp values at very low temperatures. Also, the y values obtained were compared with the DOS calculated by the DV-Xa molecular orbital method [4], In addition, the Debye temperature, the standard entropy of formation, the electric resistivity p and the thermal conductivity k were further determined for each compounds. The physico-chemical properties of the compounds were discussed from both views of the electronic and lattice vibration states. 

Hutchens et al. (1969) determined the heat capacities of zinc insulin at 0 and 0.04 h and of chymotrypsinogen A at 0 and 0.107 h, from 10 to 310 K. For all samples the data were a smooth function of temperature, with no indication of a glass or phase transition at any temperature. The absence of a phase transition corresponding to the ice-liquid water transition is expected for low hydrations. These appear to be the only data in the literature that have been used to determine the entropy of a protein sample. Hutchens et al. (1969) calculated the standard entropy of formation of a peptide bond as 9.0—9.3 cal K mol" . 

A long time ago chemists realized that the most efficient way to store thermodynamic data on chemical reactions is by making tables of standard thermodynamic properties of species. The NBS Tables of Chemical Thermodynamic Properties (4) gives AfG°, Af// and Sm° for species at 298.15 K at xero ionic strength. Since the standard molar entropy is not available for many species of biochemical interest, the standard entropies of formation Af S" are used. This property of a species is calculated by using... 

R. A. Alberty, Standard molar entropies, standard entropies of formation, and standard transformed entropies of formation in the thermodynamics of enzyme-catalyzed reactions, J. Chem. Thermodyn., in press. 

Thus Af G ° for a species in aqueous solution can be determined calorimetrically. The standard entropy of formation of a species at 298.15 K is related to its standard molar entropy at 298.15 K by... 

Module[ dGzero, dHzero, zl, nH ( This program is used to calculate the standard entropy of formation of the single species of a reactant in kj K -1 mol -1 at 298.15 K and zero ionic strength. The reactant name should be in quotation marks. The output is a 1x4 matrix. ) dGzero, dHzero, zi, nH =Transpose[speciesmat] ... 

The standard entropies of formation for species of these reactants are shown in Table 15.1. 

The values of zj and A h 0) identify the species. A longer list of standard entropies of formation is given in reference (8). 

Whenever the standard entropy of formation of a species is known, its standard molar entropy can be calculated using equation 15.3-3. This calculation is carried out using calcentropy298 (8). 

K and zero ionic strength from the standard entropy of formation of the... 

---