Those entropies of transition are calculated from Eq. If we want to calculate the entropy of a liquid, a gas, or a solid phase other than the most stable phase at T =0, we have to add in the entropy of all phase transitions between T = 0 and the temperature of interest (Fig. Self-Test 7.6B Calculate the standard molar entropy of freezing of benzene at its freezing point (see Table 6.2). The values of the absolute standard molar entropies of the ions in Table 2.15 are derived by using the data from Tables 2.13 and 2.14 in equations (2.51) and (2.57). Table 2.15 gives the absolute molar entropies for the ions under consideration. Work done with electrochemical cells, with particular reference to the temperature dependence of their potentials, has demonstrated that an accurate value for S (H h, aq) is - 20.9 J K mol-1. Table 2.15 Absolute standard molar entropies for some aqueous ions (in J K" mol - ). The conventional standard molar entropies of some anions and some elements are given in Table 2.14. Table 2.13 Standard molar entropies of some main group elements and the conventional standard molar entropies of their aqueous cations at 25 C (in J K 1 mol- ). Enthalpies of solution are positive but close to zero, within error approximation. īy applying equation 9.97 to plots of the type shown in figure 9.15B, Lux (1987) obtained standard molar enthalpies AH° and standard molar entropies ASf of solution of noble gases in melts, as listed in table 9.8. Lower part of table exchange reactions adopted with equation 3.85 (from Helgeson et al., 1978) and Sj finite differences for structural oxides (Holland, 1989). Column III = equation 3.86 with procedure of Holland (1989). Column I = simple summation of standard molar entropies of constituent oxides. Table 3.6 Comparison of predictive capacities of various equations in estimating standard molar entropy T = 298.15 K, P = 1 bar). Table 14-2 Standard Molar Entropies (S°) of Selected Substances at 298 K. Appendix D contains a more extensive list. Table 14-2 lists representative values of S to give you an idea of the magnitudes of absolute entropies. The same thermodynamic tables that list standard enthalpies of formation usually also list standard molar entropies, designated S °, fbr T - 298 K.
The molar entropies of many pure substances have been measured at standard thermodynamic conditions, P ° = 1 bar. At any higher temperature, the substance has a positive entropy that depends on the conditions. At 0 K, any pure perfect crystal is completely constrained and has S = 0 J / K. The third law of thermodynamics establishes a starting point for entropies. TABLE 7.2 Standard Molar Entropy of Water at Various Temperatures. Standard molar entropy table Standard molar entropies of elements, compounds, and aqueous ions are listed in Table 17.1 (p.
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