Entropy change during complexation

In most of these investigations only the change in free energy for the various complex formation reactions was determined. The purpose of these measurements was in most cases only to decide, via the stability constants, which species actually existed in solution. During recent years there has been an increased interest in the magnitude of the enthalpy and entropy changes for complex formation reactions. 

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. 

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