Galvani potential/voltage

According to the exact position of the equilibrium galvani potential for Ca2+-ions on the voltage axis, stimulation or inhibition of the Na+—K+ exchange can be understood. The effect of anions (e.g., MgATP2-) may be similiar as shown in Fig. 4. 

Thus, the Volta potential may be operationally defined as the compensating voltage of the cell of Scheme 16. However, it should be stressed that the compensating voltage of a voltaic cell is not always the direct measure of the Volta potential. The appropriate mutual arrangement of phases, as well as application of reversible electrodes or salt bridges in the systems, allows measurement of not only the Volta potential but also the surface and the Galvani potentials. These possibilities are schematically illustrated by [15]... 

The Galvani potential, 0, of a phase defines the amount of electrical energy, e, required to transport a charge e from an infinitely distant point in a vacuum to a hypothetical point in the interior of the phase where the charge would experience no chemical forces exerted on it. Thus the Daniell cell voltage can be written as ... 

An especially simple example of Galvani potential differences is the so-called contact potential dijference (or contact voltage) between two metals. The electrons e in a metal can be assigned a chemical potential, similar to ions in a solution. In this case it is the electron potential (We will only attach an index indicating charge such as etc., to formulas and names of substances when it is necessary or useful for clarity. Expressions like e and e will be treated as equal.) will be different depending upon the metal in question. 

Galvani voltage 17i n then forms between the solution (phase I) and the inert metal (phase II), exactly as it would form between two metals (Fig. 22.3). We can calculate the Galvani potential difference or the Galvani voltage, respectively, according to Eq. (22.8) or Eq. (22.9), by inserting the value of the electron potential in the metal, here the commonly used platinum (Pt), and of the redox pair Rd/Ox in the solution (S),... 

In the aforementioned discussion of Eqs. (2) and (3), the solution composition was considered to be fixed. A comparison of the data for different electrolyte concentrations opens a way to extract extensive additional information on the interfacial properties on the basis of the Gibbs thermodynamics. To exploit this possibility one has to deal with electrode potentials (instead of the Galvani potential). This quantity is defined as the voltage between the working electrode and the reference electrode immersed to the same solution and reversible with respect to one of its ionic components, for example, E for such cation- or... 

When applying a voltage on the EC a part rj of this voltage appears across the interface and modifies the Galvani potential drop there. The modification is generated by a change of the double-layer charge. 

When one of these Galvani potential differences, e.g. A< is kept constant, this electrode can be used as a reference electrode. Then, the relative electrode potential of an electrode (indicated here as X) is the cell voltage of a galvanic cell, which consists of the electrode and the reference electrode (R). 

Fig.II.9.1 Cell voltage E as the sum of the Galvani potential differences for two metal electrodes in the same electrolyte solution. Superscript Sol indicates the solution and Me indicates the metal...

The equilibrium is only reached once the Galvani potential and the chemical potentials of each type of species are both identical in the two phases. The junction voltage is therefore zero in equilibrium, which indeed can take a long time to reach. 

Moreover, the difference between the surface electric voltages in the two phases is overlooked (see section 3.1.1.2, Xa = X >- Therefore, the Volta and Galvani potential differences between the two phases are considered as being equal ( > - a= a)-... 

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