Concentration Profiles in Ideally Labile Systems

The usage of simple relationships Eqs. (3.26) and (3.27) is very tempting, because the solutions of such equations supplemented with corresponding initial and boundary conditions have been well-expounded in literature. However, no information concerning individual components of the system follows from these equations. Therefore, to obtain such data, it is necessary to formulate extra interrelations between their concentrations. 

When the chemical interactions between complexes and ligands proceed with a sufficiently high rate, it is common to treat their concentrations as close to equilibrium ones. Assumptions of such kind have been of frequent use and can be found in different problems of electrochemical kinetics. Then, the relations between concentrations might be determined by cumulative (fij) or stepwise (Kj) stability constants of complexes and protonated ligands. An expression for Pj is given in Chapter 1 stepwise equilibria, such as (3.16) and (3.17), can be characterized by 

Further, we shall designate such systems as ideally labile (IL systems). 

On the basis of the aforementioned conclusions, equations adapted to the diffusion layer acquire the following expression  

Steady-state problems are simplest, because i values, like concentration profiles, are independent of t. Then the analog of Eq. (3.6) applies 

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