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In electrochemistry, electrode potential is the voltage of a galvanic cell built from a standard reference electrode and another electrode to be characterized. [1] By convention, the reference electrode is the standard hydrogen electrode (SHE). It is defined to have a potential of zero volts. It may also be defined as the potential difference ...
The electric potential also varies with temperature, concentration and pressure. Since the oxidation potential of a half-reaction is the negative of the reduction potential in a redox reaction, it is sufficient to calculate either one of the potentials. Therefore, standard electrode potential is commonly written as standard reduction potential.
Electrode potentials of successive elementary half-reactions cannot be directly added. However, the corresponding Gibbs free energy changes (∆G°) must satisfy ∆G° = – z FE°, where z electrons are transferred, and the Faraday constant F is the conversion factor describing Coulombs transferred per mole electrons. Those Gibbs free energy ...
A reference electrode is an electrode that has a stable and well-known electrode potential. The overall chemical reaction taking place in a cell is made up of two independent half-reactions , which describe chemical changes at the two electrodes.
Then one looks up the standard electrode potential, E o, in volts, for each of the two half reactions. The standard potential of the cell is equal to the more positive E o value minus the more negative E o value. For example, in the figure above the solutions are CuSO 4 and ZnSO 4.
During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it could actually be constructed by "[immersing] a platinum electrode into a solution of 1 N strong acid and [bubbling] hydrogen gas through the solution at about 1 atm pressure".
Potentiometry passively measures the potential of a solution between two electrodes, affecting the solution very little in the process. One electrode is called the reference electrode and has a constant potential, while the other one is an indicator electrode whose potential changes with the sample's composition. Therefore, the difference in ...
For example, for oxygen, the species would be in the order O 2 (0), H 2 O 2 (–1), H 2 O (-2): The arrow between O 2 and H 2 O 2 has a value +0.68 V over it, it indicates that the standard electrode potential for the reaction: O 2 (g) + 2 H + + 2 e − ⇄ H 2 O 2 (aq) is 0.68 volts.