General Features of Electrode Processes

A special kind of chemical reactions are the redox (reduction-oxidation) processes in electrochemical circuits - the systems consisting of two metal electrodes in solution of electrolyte (internal circuit) that are coimected using an electronic conductor (external circuit). Electrolytic and Galvanic cells are the examples of electrochemical circuits. The reactions occurring in such cells are called electrochemical reactions to stress out their essential difference from ordinary chemical processes. 

An elementary act of a traditional homogeneous redox reaction can be considered as a collision of the reacting particles with a simultaneous electron transfer from the reductant to the oxidant. This approach does not work with electrochemical processes. Here, the reactant and the oxidant are separated in space and the electron transfer occurs through the external circuit. Thus, an electrochemical reaction is accompanied by electron flow. The directed electron flow might be induced by a spontaneous reaction in the circuit. In this case, one deals with a Galvanic cell. On the craitrary, in an electrolytic cell, the electric current from an external source may cause non-spontaneous chemical transformations. 

The overall reactirai in electrochemical circuit consists of two half-reactions reduction and oxidation. Each of them takes place on a separate electrode - a metallic conductor immersed into electrolyte solution. The electrode where oxidation occurs is called anode. Another electrode, where the reduction takes place, is called cathode. 

The Faraday laws of electrolysis are quantitative relationships between the amount of substance chemically transformed on an electrode and the amount of electricity that passed through the electrochemical circuit. For example, the same amount of electricity - 96,485 C - is required for a reaction of 1 mEq of any compound. The following equation is commOTily used in calculations  

Korobov and VJF. Ochkov, Chemical Kinetics with Mathcad and Maple, DOI 10.1007/978-3-7091-0531-3 5, Springer-VerlagAVien 2011 

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