Electrode potentials and oxidation state diagrams

In calculating the cell potential of an electrochemical cell and to calculate the maximum possible energy produced one uses the expression 

In fact, each electron transfer half-reaction involves a free energy change following this formula. To reach the total variation in AG we sum the contributions of the two half-reactions, remembering that one is a reduction and the other an oxidation. For example, for the dissolution of silver chloride under standard conditions 

This value of K can be identified with the solubility product—the differences that arise in relation to tabulated values of Ksp are due to differences in the solution conditions. In the same way we can calculate stability constants of complexes. 

Some conclusions can be drawn from these diagrams  

The diagrams are normally constructed in relation to the hydrogen electrode with aH+ = 1 as reference, which would be a horizontal straight line. However, they can be modified for the reference to be another pH or another half-reaction. If we choose as reference the reduction of oxygen to water under standard conditions, for example, which has e =+ 1.23 V, the modification corresponds to a clockwise rotation of the diagram. 

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