Potential difference between two phases

Thus Pi, surface potential jump X, the chemical potential p, and the Galvani potential difference between two phases A0 = are not. While jl, is defined, there is a practical dif-... 

In addition to the case of a metal in contact with its ions in solution there are other cases in which a Galvani potential difference between two phases may be found. One case is the innnersion of an inert electrode, such as platinum metal, into an electrolyte solution containing a substance S that can exist m either an oxidized or reduced fomi tlirough the loss or gain of electrons from the electrode. In the sunplest case, we have... 

From the viewpoint of the chemical engineer, the application of the fundamentals just discussed takes the form of mass-transfer theory, and the constants Kj are called mass-transfer coefficients. However, some care must be exercised in determining the potential difference between two phases. One cannot simply take the difference between the thermodynamic activities in two phases without ensuring that they are adjusted to the same reference state. The point is illustrated with a brief consideration of the boundary-layer model. 

Indeed, this solvent-size correction for the chemical potentials worked well in the initial COSMO-RS parameterizations, yielding quite small values of in the region of -0.14. Thus it appeared that the two different size contributions almost cancel out, i.e., only 14% of the obvious first contribution remains. Even large size differences of up to a factor of 10 in surface area only yielded corrections of 0.8kJ/mol in the chemical potential differences between two phases these corrections were only about half of our standard deviation at that time. Therefore, not much care was taken with respect to the combinatorial contribution during the next years of COSMO-RS development. All other contributions appeared to be of much greater importance. 

It may be convenient to regard the Galvani potential difference between two phases in contact as being due to two effects the orientation of dipoles in the interface between them and the separation of independently mobile charged species across the phase boundary in an analogous way to that discussed for the separation of (f> into outer and surface potentials [5, 6]. 

The electrostatic potential of a phase is defined as the potential of the space just outside it, for a phase a let this be Fa. The Volta potential difference between two phases is the difference in electrostatic potential between two points just outside the phases. The electrostatic potentials, and therefore the Volta potential, are determined by the amount of charge on the phase and its electrostatic capacity. 

The Volta potential difference between two phases a and j3 is Fa— F it is sometimes called the external contact potential, more commonly simply the contact potential. 

Galvani (inner) potential difference between two phases i, j... 

GuggenheimE. A. (1929), The conceptions of electric potential difference between two phases and the individual activities of ions , J. Phys. Chem. 33, 842-849. 

E.A. Guggenheim The conceptions of electrical potential differences between two phases and individual activities of ions. Journal of Physical Chemistry 33 (1929), p. 842. 

Equilibrium concentration calculations based on the calculation of the Galvani potential difference between two phases was developed in the previous papers [1,2]. This chapter will systematize the theoretical distribution equilibrium calculation presented in Refs 1 and 2, evaluate how well the electrochemical concept is able to be applied to the study of the liquid - liquid extraction process, and establish the problem for the most general case where arbitrary interactions occur in the system. 

If it is accepted that an electrochemical reaction is one where the Gibbs energy of the reaction depends on the potential difference between two phases, as well as temperature and pressure (as do classical chemical reactions), then charge transfer reactions at soft interfaces are truly electrochemical reactions. Indeed, their characteristic is to be potential-dependent and controlled by the Galvani potential difference between the two phases in contact. 

It is difficult to measure the potential difference between two phases such as an electrode and a solution. This is because a minimal measuring circuit must involve at least two boundaries. If you have two different electrodes in a liquid, you have two electrode/solution boundaries. Any potential that you measure cannot be unambiguously attributed to one particular electrode/solution... 

Absolute value of the Galvani potential difference (electrical potential difference between two phases)... 

Although admittedly the potential difference between two phases is not accessible to direct experimental determination, it is important to investigate whether the x-potential can be approached by model considerations ... 

According to 3d, p- 126, the potential difference between two phases in equilibrium is related to the chemical potentials of the potential-determining ions by the eq. 

The significance of eq. (1) might seem doubtful to the reader who remembers that the potential difference between two phases is not accessible to experimental determination. It should, however, be pointed out that changes in this potential difference can be determined experinicntally and, given our definition of the ero point of is in fact only a change in the potential difference between two phases. For a more detailed discussion of this question the reader is referred to chapter IV 3, p. 118. 

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