ABSTRACT
This chapter briefly mentions some equilibria in solutions and retains those involving the formation of complexes, the partition of solutes between two non-miscible solvents and also the so-called osmotic work in biological systems. Numerous comments can be made about the complexes. They concern their physico-chemical behavior in aqueous solutions, in particular the quantitative features of their formation and dissociation. Many biochemical reactions indeed involve the formation of complexes in quantitative way, thus making difficult the foreseeing of the course of some of their reactions. From the quantitative standpoint, half reactions are governed by dissociation constants Kc. They are introduced to maintain the similarity with the redox and acido-basic equilibria. Complexation reactions can be foreseen as are, for example, the acid-base ones. Partition equilibria certainly occurs in cells, owing to the presence of several phases. To be convinced by this fact, it suffices to recall the structure and properties of cell membranes.
