Equilibrium between Phases in Electrochemical Cell

Earlier, in this book, it was shown that if two phases are in equilibrium (e.g., dissolved electrolyte and solid salt of this electrolyte or electrolyte solvent and solvent in vapor phase), the Gibbs energies of formation of the solution components should be same in both phases. Fundamentally, there is equilibrium between phases a and p if the chemical potentials (the Gibbs energies of formation) of any of the fth component in both phases are equal  

John Frederic Daniell (1790-1845) was an English scientist who is well known for his invention of the Daniell cell, which is one of the earliest prototypes of electric batteries. The Daniell cell consists of two metal, copper and zinc, electrodes and is a classical electrochemical system conunonly used in electrochemical education. 

Inzelt, and F. Scholz, Electrochemical Dictionary, Springer, Berlin, Germany, 2008. 

In an electrochemical system with phases a and p, the criterion of equilibrium should be modified due to different electric potentials cp and respectively, in phases a and p. As an example, let us consider zinc electrode of the Daniell cell, which was introduced by John Frederic Daniell in 1836. Think of a piece of zinc metal being dipped into a dilute solution of ZnS04(aq). Between the solution and metal phases, aqueous zinc ions, Zn +(aq), can be transferred. If the initial solution is extremely dilute, then the rate of transfer of ions from the metal to the solution is faster than the transfer from the solution to the metal. When Ztf+(aq) leaves the metal surface, electrons are left behind because they cannot enter the solution. This builds up a negative electric potential in the metal phase. After some time, an equilibrium state is reached between the so-called electrochemical potential of Zn +(aq) within the metal and solution phases. The electrochemical potential of the species in each phase comprises two components (1) the chemical potential of the species p, and (2) the electric 

Luigi Aloisio Galvani (1737-1798) was an Italian scientist who was the first to introduce bioelectrochemistry to study the nature of electrical effects on animal tissues. 

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