Cell potential electrical work, and free

Cell Potential, Electrical Work, and Free Energy... 

The equals sign is valid for a reversible i —> 0) conversion the greater than sign is valid for an irreversible conversion (finite i). Hence, an electrochemical cell delivers electric work equal to the free energy ehange only at infinitesimal current flow under these eonditions the cell potential is the OCV and the electric work delivered is the maximum ITei max = nPVoc = -AG (n is the number of moles of transferred electrons and Fthe Faraday constant). 

Relating the free energy change to electrical work and cell potential (701) ... 

We now consider briefly the matter of electrode potentials. The familiar Nemst equation was at one time treated in terms of the solution pressure of the metal in the electrode, but it is better to consider directly the net chemical change accompanying the flow of 1 faraday (7 ), and to equate the electrical work to the free energy change. Thus, for the cell... 

An electrochemical cell generates a potential difference E. (The symbol E, commonly used in electrochemistry, refers to electromotive force, an archaic term for potential difference.) The electrical work done when n moles of electrons is passed by the cell can be found using Eq. (15-1), w = -nFE. It can be shown that the electrical work done by an electrochemical cell, at constant temperature and pressure, is equal to the change in Gibbs free energy of the cell components,... 

Recall that free energy is related to the maximum possible amount of work that can he done hy the system. In the case of a galvanic cell, the work done is electrical work, so we can state the relationship between fi-ee energy and the cell potential as... 

For a given electrochemical reaction, the theoretical open-circuit voltage, the Nernst potential, is an important, if not the most important, parameter that affects and measures a fuel cell s performance. The Nernst potential is affected by the operating conditions of the SOFC, such as the temperature, pressure, and fuel composition, and is calculated from the maximum electrical work obtainable, the Gibbs free energy of the reaction (AG) ... 

The maximum amount of electrical work that can be done by an electrochemical cell is equal to the Gibb s free energy change (Chapter 15), AG (provided the temperature and pressure remain constant). The equation below gives the exact relationship between the Gibb s free energy and the cell potential ... 

For n eleetrons, the electrical work performed is nFE, where F is Faraday s constant and E is the cell voltage. This represents the action of moving an electrical charge through an electrical potential field. Under reversible conditions, where no net current flows, the maximum electrical woric is performed (nEE°), where E° corresponds to the thermodynamic cell voltage. When maximmn work is performed, this corresponds to the change in free energy (AG) for the reaction, and consequently ... 

V are the electrical potentials in masses of the same kind of metal connected with the anode and cathode respectively . Also, tdri=dOt the heat absorbed by the cell, and at constant temperature de — M17=d0, where — the free energy (so called by Helmholtz) hence at constant temperature the electrical work (V - V")de is not strictly equal to the decrease of energy - dc, as the Helmholtz-Thomson (see p. 690) rule stated, but to the decrease of free energy — d. If the pressure as well aa the temperature is constant, the electrical work is - d, when C—e — trj +pv,... 

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