Entropy change overall

FIGURE 7.18 In an exothermic reaction, (a) thp overall entropy change is certainly positive when the entropy of the system increases. (b)The overall entropy change may also be positive when the entropy of the system decreases. The reaction is spontaneous in both cases. 

There is also an entropy term associated with the desolvation of the ligands. This is much more difficult to assess, and may make for either favourable or unfavourable contributions to the overall entropy changes. 

In words, in any process that occurs at constant T and P, the free energy change for the system is negative whenever the total entropy change is positive that is, whenever the overall process is spontaneous. Defining a new function and imposing some restrictions provides a way to use properties of a system to determine whether a process is... 

C14-0121. Apiece of dry ice at T = 195 K is dropped into a beaker containing water at T = 273.15K.You may assume that all of the resulting CO2 vapor escapes into the atmosphere, (a) Describe the process that takes place at the molecular level, (b) Calculate the overall entropy change if 12.5 g of diy ice undergoes this process. 

For several reversible reactions, the thermodynamic parameters for reaction in the quasi-free state are given in Table 10.6 using Eq. (10.16) and the reaction scheme (I). Experimental data for AX°(X = G, H, or S) are taken from Holroyd et al., (1975, 1979) and Holroyd (1977), while Table 10.5A provides data on AX r°, except for TMS (vide supra). The chief uncertainty in these calculations is the experimental determination of V0. It is remarkable that all thermodynamic parameters of reaction in the quasi-free state are negative in the same way as for the overall reaction. In particular, the entropy change is relatively large and probably for the same reason as for the overall reaction (Holroyd, 1977). 

A Schottky defect in a crystal consists of a cation and anion vacancy combination that ensures overall electroneutrality in the crystal (Section 1.9). The estimation of the configurational entropy change in creating a population of Schottky defects in a crystal can be obtained in the same way as that of a population of vacancies in a monatomic crystal. The method follows that given in Section 2.1 for the equilibrium concentration of vacancies in a monatomic crystal and is set out in detail in Supplementary Material S4. 

In a crystal of overall composition MX, suppose that ns is the number of Schottky defects in the crystal at a temperature T (K), that is, there are ns vacant cation sites and ns vacant anion sites present, distributed over N possible cation sites and N possible anion sites. The configurational entropy change, ASs, due to the distribution of the... 

The overall entropy change is positive, which confirms that the reaction Is feasible. 

The overall enthalpy and entropy changes for the distribution reaction (i.e., transfer of the metal complex from the aqueous to the organic phase) can be obtained from the temperature dependence of A r according to... 

Based on this somewhat simplified picture, overall enthalpy (A/finc,usion) and entropy changes (ASindusion) relevant to the inclusion are calculated by using Eqs. (2) and (3), respectively, where subscripts c, w, and g refer to inclusion complex, water molecules, and guest molecule, respectively ... 

In phase change processes, the overall entropy changes,, can be understood by considering the degrees of freedom lost when molecules in one condition (e.g., as a liquid) are packed into a less free, new condition (e.g., as a solid). Such transformations have been viewed as involving three contributions to the change in molecular freedom (1) positional, (2) conformational, and (3) rotational (Yalkowsky, 1979 Dannenfelser and Yalkowsky, 1996) ... 

---