Liberational entropy

This is equivalent to the definition of liberational entropy given by Go et 2l 20.21.100... 

The hydrophobic effect. Water molecules around a non-polar solute form a cage-like structure, which ices the entropy. When two non-polar groups associate, water molecules are liberated, increasing the entropy. 

The theory predicts high stabilities for hard acid - hard base complexes, mainly resulting from electrostatic interactions and for soft acid - soft base complexes, where covalent bonding is also important Hard acid - soft base and hard base - soft acid complexes usually have low stability. Unfortunately, in a quantitative sense, the predictive value of the HSAB theory is limited. Thermodynamic analysis clearly shows a difference between hard-hard interactions and soft-soft interactions. In water hard-hard interactions are usually endothermic and occur only as a result of a gain in entropy, originating from a liberation of water molecules from the hydration shells of the... 

The reaction favours the formation of ozone with a significant equilibrium constant. Appendix C also lists the enthalpies of formation and the standard enthalpy of the reaction ArH° can be calculated. The answer for the enthalpy calculation is ArH° = —106.47 kJ mol, showing this to be an exothermic reaction, liberating heat. The entropy change at 298 K can also be calculated because ArG° = ArH° — T ArS°, so ArS° = 25.4 Jmol-1 K-1, indicating an increase in the entropy of the reaction as it proceeds by creating one molecule from two. 

As hydrophobic surfaces contact each other, the ordered water molecules that occupied the surfaces are liberated to go about their normal business. The increased entropy (disorder) of the water is favorable and drives (causes) the association of the hydrophobic surfaces. 

The second important solvent effect on Lewis acid-Lewis base equilibria concerns the interactions with the Lewis base. Since water is also a good electron-pair acceptor129, Lewis-type interactions are competitive. This often seriously hampers the efficiency of Lewis acid catalysis in water. Thirdly, the intermolecular association of a solvent affects the Lewis acid-base equilibrium242. Upon complexation, one or more solvent molecules that were initially coordinated to the Lewis acid or the Lewis base are liberated into the bulk liquid phase, which is an entropically favourable process. This effect is more pronounced in aprotic than in protic solvents which usually have higher cohesive energy densities. The unfavourable entropy changes in protic solvents are somewhat counterbalanced by the formation of new hydrogen bonds in the bulk liquid. 

The values of JSn generally decrease as the metal ion becomes larger and its effective charge lower, i. e. as the electric field around the metal ion becomes weaker. This is certainly to be expected as a weaker field implies less well-ordered inner an outer hydration shells and consequently less increase of entropy when the water molecules are liberated. 

Figure 5.1 (a) The aggregation of surfactant molecules showing the increase of entropy due to the liberation of water molecules. Hydrophobic forces are the main factors for the association of surfactant molecules, (b) The analogy with two droplets of oil in water. 

Figure 15. Schematic drawing of complexation-induced desolvation from cation and ligand (solvation to the latter is not shown) the complex formation itself reduces the entropy of the system to some extent but the accompanying desolvation leads to much larger increase in entropy ascribed to the liberation of solvent molecules.

We have seen that while many spontaneous processes, e.g., combustion of organic compounds, are accompanied by liberation of heat (negative AH), others are accompanied by absorption of heat from the surroundings (positive AH). An example of the latter is the melting of ice at a temperature just above 0°C, during which there is a large increase in the entropy of the water. As we have seen, at 0°C at equilibrium T AS is just equal to -AH (Eq. 6-7). 

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