PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 403

where Φoxis the potential of the anode (on which oxidation occurs), and Φredis the potential
of the cathode (on which reduction occurs). The same relation applies for the standard cell
potential and the standard electrode potentials

E◦= Φ◦ox+ Φ◦red. (11.126)

In view of relations (11.124) we can rewrite equations (11.125) and (11.126) to the forms in
which only reduction potentials appear

E=−Φred(anode) + Φred(cathode), E◦=−Φ◦red(anode) + Φ◦red(cathode). (11.127)

Note:Equation (11.125) and the first of equations (11.127) apply only for galvanic cells

with one electrolyte and for cells without transference. For cells with transference, the

diffusion potential has to be added to the cell potential.

11.8.9 Classification of half-cells

Half-cells are divided into several categories:

• A metal electrode, in which the electrolyte contains the ions of the given metal.
  These half-cells are divided into the following sub-categories:
  
  
  • amalgam,
  
  
  • first-type,
  
  
  • second-type.
  
  
  
  


• A nonmetal electrode, in which the electrolyte contains the ions of a nonmetal.
  These half-cells are divided based on the nature of the electrode:
  
  
  • gas electrode,
  
  
  • solid electrode.
  
  
  
  


• Reduction-oxidation half-cells


• Ion-selective half-cells.

11.8.10 Examples of half-cells

Presented below are some typical examples of the individual half-cell categories and sub-
categories. The reactions at the electrodes and the Nernst equation are given for reduction.