Direction of evolution of an electrochemical equilibrium. Practical consequences
Standard potentials of aqueous solutions

The electrochemical equilibrium of a system may break down when two conditions are simultaneously met:

• its composition allows it to move in one of two conventional directions:

  • Ox reduction according to :

    Ox + ne^– ® Red

  • oxidation of Red according to :

    Red ® Ox + ne^–

• it is able to exchange electrons with an appropriate reagent.

During reduction, Ox's activity must decrease and Red's increase. It follows from this (application of Nernst's law) that a reduction must be accompanied by a decrease in the couple's equilibrium potential.

Conversely, oxidation should be accompanied by an increase in this...