Thermodynamics of Electrochemical Cells

In Section 3.3.4, we discussed the inclusion of electrical (emf) contributions to the general expression for work, 

Compared with the cell-free conditions discussed previously, the internal energy changes dU must be modified by inclusion of the electrical work term  

The charge increment dQ for current I flowing through time increment dt can be measured as 

However, from a chemical viewpoint, dQ can also be expressed in terms of the electrons transferred at the electrodes for each increment di of cell reaction. For this purpose, it is convenient to write the overall redox cell reaction as separate oxidation/reduction halfreactions, expressing the loss or gain of z electrons at each electrode in the balanced cell reaction (i.e., involving z equivalents of charge transferred in oxidization and reduction steps). It is also convenient to quantify total charge in molar units (i.e., Avogadro s number NA of electrons) as expressed by the Faraday constant T, 

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In the first part, Chapters 2-6, some fundamentals of electrode processes and of electrochemical and charge transfer phenomena are described. Thermodynamics of electrochemical cells and ion transport through solution and through membrane phases are discussed in Chapter 2. In Chapter 3 the thermodynamics and properties of the interfacial region at electrodes are addressed, together with electrical properties of colloids. Chapters 4-6 treat the rates of electrode processes, Chapter 4 looking at fundamentals of kinetics, Chapter 5 at mass transport in solution, and Chapter 6 at their combined effect in leading to the observed rate of electrode processes. 

In this section we lirsi consider the thermodynamics of electrochemical cells and the relationship between the activities of ihc participants in typical cell reactions and the observed potential of the cell. We then describe the source of the junction potentials thal occur in most electrochemical cells. In Section 22C we consider the ptitentials of individual electrodes making up cells. 

This work presents electrochemistry from a macroscopic viewpoint, and is divided into 4 parts the thermodynamics of electrochemical cells, electrochemical kinetics, transport processes, and finally current distribution and mass transfer in electrochemical systems (including porous electrodes and semiconducting electrodes). Problems to solve are presented at the end of each chapter, without the answers. 

At the interface of the two electrolytes, there exists no real equilibrium situation, because of the presence of strong concentration gradients, which drive ion diffusion across the junction. After an infinitely long period of time, the concentrations would become uniform from one part of the junction to another. However, the presence of a frit or membrane slows down the diffusion phenomena enough to keep the liquid junction in place during a long time. Despite this, the inherent instability of liquid junctions remains the main source of difficulty for those who attempt to rigorously describe the thermodynamics of electrochemical cells. 

The thermodynamics of electrochemical cells is treated in all textbooks of physical chemistry as are the conventions. The discharging lead-acid battery would commonly be written as the cell ... 

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