17. The Drive To Make Things       Happen   Previous PageNext Page
      Redox Reactions and Electrochemical Potential

In exactly the same way, we can define the electrochemical potential of a cell using oxidation-reduction reactions as the free energy change per mole of electrons transferred. If one mole of reaction occurs with the transfer of n moles of electrons (n = 2 in the Zn-Cu cell), and if F is the charge on one mole of electrons, then the electrochemical potential, E, is given by

D G0 =-nFE0

The superscript 0 on the potential, E0, has the same meaning as for free energy. It signifies the value when reactants and products all are in standard states of 1-molar concentrations, or 1-atm partial pressures for gases. It usually also refers to a temperature of 25° C.

The charge on a mole of electrons, F, is known as Faraday's constant. It has various numerical values, depending on the units involved, but if free energy is in kcal mol-1, n has units of electrons, and potential is expressed in volts, then F= 23.056 kilocalories per mole per electron volt (eV), or 23.056 kcal mol-1 eV-1.

Example. What is the standard electrochemical potential of the ZnCu cell?


   Page 31 of 56 HomeGlossary