Cell potential variation with

Since concentration variations have measurable effects on the cell voltage, a measured voltage cannot be interpreted unless the cell concentrations are specified. Because of this, chemists introduce the idea of standard-state. The standard state for gases is taken as a pressure of one atmosphere at 25°C the standard state for ions is taken as a concentration of 1 M and the standard state of pure substances is taken as the pure substances themselves as they exist at 25°C. The half-cell potential associated with a halfreaction taking place between substances in their standard states is called ° (the superscript zero means standard state). We can rewrite equation (37) to include the specifications of the standard states ... 

We see from this equation that the actual potential produced by an electrochemical cell involving a hydrogen (or hydronium) ion depends linearly on the pH of the solution. The total cell potential also depends on the activity pf the metal ion in the other halfcell, which usually would be approximately constant, and the activity of molecular hydrogen, which can be controlled by its partiarpressure. Consequently, the primary variation of the cell potential is with pH.-This result suggests that an electrochemical cell can be used to measure the pH of a solution. This is actually done in the laboratory, but by using specially chosen liquid electrodes rather than a hydrogen gas electrode, which is not convenient to use.. ... 

CATALYST WORK FUNCTION VARIATION WITH POTENTIAL IN SOLID ELECTROLYTE CELLS... 

Wagner, 7 Wolkenstein, 279 Work function and absolute potential, 353 and electrochemical promotion, 138 and cell potential, 138, 218 Helmholtz equation, 24 of metals, 139 measurement of, 138 spatial variations, 222 variation with coverage, 24 Working electrode as catalyst, 9 overpotential of, 123... 

Since the reaction in the working electrode is an oxidation when the overall reaction is (7.14), the cell potential in (7.15) is defined as = ,ork - ref = anode Scaihode and the sign in this equation is opposite to that obtained with the more common convention that defines the cell potential as = caUiode - T anode ) From the temperature variation of the cell potential, the following equation can be written for the entropy of the overall reaction ... 

Numerical solution of Chazelviel s equations is hampered by the enormous variation in characteristic lengths, from the cell size (about one cm) to the charge region (100 pm in the binary solution experiments with cell potentials of several volts), to the double layer (100 mn). Bazant treated the full dynamic problem, rather than a static concentration profile, and found a wave solution for transport in the bulk solution [42], The ion-transport equations are taken together with Poisson s equation. The result is a singular perturbative problem with the small parameter A. 

Electrochemical Cells A Qualitative Discussion of the Variation of Cell Potential with Current... 

If it is recalled that on a purely thermodynamic basis, any cell that has a tendency to drive a current through an external load seems capable of being harnessed as an energy-producing device, then the conclusion just reached is serious, for it bears the following implication In the development of an energy-producing device, the variation of cell potential with cell current is as important as, if not more important than,... 

This is the transient method for which most experience is available. It was introduced by Bowden and Rideal (1928). The name comes from that of Galvani4 and means, in fact, current. Thus, Galvanostatic transient means short-term constant current. The circuitry is simple. It consists of nothing more than a measurement cell in series with an adjustable resistance much larger in value than the resistance of the cell, a power source, a rapid action switch, and a cathode ray oscilloscope to record the variation in the potential of the working electrode with time. A typical potentialtime relation is shown in Fig. 8.6. 

The variation of cell potential with composition is expressed by the Nernst equation, Eq. 7. 

Fig. 16. Top The illustration shows the variation of the induced transmembrane potential of a cell with frequency and with the conductivity of the external medium. The induced potential increases with external conductivity. However, it also decreases with frequency and above about 5 or 10 MHz the induced potential has fallen below 10 mV in most practical cases. Cells can be cultivated for days in fields of high MHz frequencies.

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