Entropy during complexation

The term stable complex is defined in terms of the equilibrium eonstant for the formation of the complex. The equilibrium constant of a reaction is a measure of heat released in the reaetion and the entropy ehange during the reaetion. The greater the amount of heat evolved in a reaction the more stable are the reaetion products. The entropy of a system is a measure of the amount of disorder. The greater the amount of disorder in the products of a reaction relative to the reactants, the greater the increase in entropy during the reaction... 

By performing calorimetry during complex formation it has been found that the enthalpy of complex formation of systems that form glass-like phases has an opposite sign to the enthalpy of systems that form liquid-like phases, i.e., the formation of glass-like phases is exothermic and the formation of liquid-like phases is endothermic. The free energy (AfG), enthalpy (Af//) and entropy (Af5) of polyelectrolyte complex formation and how they vary as a function of the ionic strength will be discussed. 

The maxima of AS at 20 °C and 30 °C in the mixed solution of PMAA and POE with molecular weight of 2000 and 3000 are related to the entropy change at complex formation (Fig. 12.8). Positive values of dS in aqueous systems suggest the release of water during complexation. The complexation system of PMAA and POE with a molecular weight of 20000 does not exhibit any pronounced values of AH and AS, This shows that a complex was already formed in the temperature range that was not investigated. 

After their release from solvating this chloride ion, each water molecule has as much energetic disorder as did the whole chloride ion complex. Therefore, we expect a sizeable increase in the entropy of the solvent during crystallization because many water molecules are released. 

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