Symbols and normalisation

In a complex mechanism, many chemical species may be involved and our system of symbols like C, C, etc, for the concentrations of species A, B, etc, becomes a little awkward. Nevertheless, we stick with it because the alternatives lead to overlap with other symbols, already in use. Concentrations are normalised by the bulk concentration Cj of a particular species, usually the first one to undergo an electrochemical reaction and present initially. 

Chemical reactions produce extra terms in the diffusion example, a following reaction scheme (EC) like 

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