Galvanic cells, theory

Nernst equation for concentration cells, 467 theorem, 484, 489, 508, 531 theory of galvanic cells, 474... 

In writing the Etudes de dynamique chimique (1884), van t Hoff drew on Helmholtz s 1882 paper but especially on the work of August Horstmann, a student of Bunsen, Clausius, and H. Landolt.59 As has often been discussed, van t Hoffs was an ambitious and original synthesis of disconnected ideas and theories about opposing forces, equilibrium, active masses, work and affinity, electromotive force, and osmotic pressure. He demonstrated that the heat of reaction is not a direct measure of affinity but that the so-called work of affinity may be calculated from vapor pressures (the affinity of a salt for its water of crystallization), osmotic pressure (affinity of a solute for a solution), or electrical work in a reversible galvanic cell (which he showed to be proportional to the electromotive force). 

In 1848 du Bois-Reymond [21] suggested that the surfaces of biological formations have a property similar to the electrode of a galvanic cell and that this is the source of bioelectric phenomena observed in damaged tissues. The properties of biological membranes could not, however, be explained before at least the basic electrochemistry of simple models was formulated. The thermodynamic relationships for membrane equilibria were derived by Gibbs in 1875 [29], but because the theory of electrolyte solutions was formulated first by Arrhenius as late as 1887, Gibbs does not mention either ions or electric potentials. 

Of the Mechanical Origin of Corrodibility , which appeared in 1675 in London.2 It was not until the turn of the 19th century3,4 that some of the basic principles were understood, soon after the discovery of the galvanic cell and Davy s theory on the close relationship between electricity and chemical changes.5... 

Fuoss theory for ion association I.S.2d Galvani potential see potential galvanic cells 1.5.Se gases. 

These equations are of great importance in chemistry and physics. They were first derived by Helmholtz and independently by Willard Gibbs in connection with the theory of galvanic cells. The former of the two equations is the more generally useful in chemistry, since it is easier as a rule to keep the pressure on a system constant than to maintain it at constant volume. We shall have frequent examples of the-application of equation (21) in the subsequent chapters of this book. 

The galvanic cells discussed hitherto (of the first kind) owe their power of yielding electrical energy to the forces of chemical affinity. A second type of cell makes use of the dilution tendency of dissolved substances (osmotic pressure). Galvanic cells of this type are called concentration cells. The thermodynamical theory of these cells was initiated by Helmholtz, and completed later on by Nernst. 

When using the specific ion interaction theory, the relationship between the redox potential of the couple PuO /Pu " in a medium of ionic strength /, and the corresponding quantity at / = 0 should be calculated in the following way. The reaction in the galvanic cell ... 

Volta s greatest contribution was, however, the discovery, in 1796. of the voltaic pile, which consisted of a series of units, each made from sheets of dissimilar metals such as zinc and silver separated by wet doth. Volta showed that metals could be arranged in au "electromotive series so that each became positive when placed in contact with the one next below it in the series. Although, as has already been mentioned, Volta considered that the source of the electric energy was at the surface of contact of, the metals, this theory was thrown in doubt when it was discovered that chemical action accompanied the operation of the pile. It is of interest that the question of the seat of the potential of the galvanic cell is not, even today, finally settled. Many improvements of the voltaic pile were made. It is, of course, the precursor of the modern galvanic cell. 

Transference numbers will also be found useful in obtaining precise values of the activities of ion constituents. It was another of Arrhenius tacit assumptions that ion concentrations may be used without error in the law of mass action. To investigate the limits of validity of that assumption, and to lay a foundation for the modern interionic attraction theory of solutions, it is necessary to consider the thermodynamics of solutions, and of the galvanic cell, subjects which are discussed in Chapters 5 and 6. 

We now turn our attention to a study of the thermodynamic theory of galvanic cells. Galvanic cells are heterogeneous systems in which current is transmitted between the phases and in which chemical reactions may occur. The terminal phases of a galvanic cell are termed electrodes, and current passes from one electrode through the other phases to the other electrode. 

The theory developed here has its most important application in the study oi reversible galvanic cells. Galvanic cells may be separated into two classes those with and those without liquid junction. In Sec. 13-2, we consider a galvanic cell without liquid junction using the necessary criterion for equilibrium [Eq. (13-23)]. In Sec. 13-3, we discuss a cell with liquid junction in terms of the complete conditions for heterogeneous equilibrium. 

It is clear from Eq. (13-105) that a knowledge of e and ci- permits evaluation of the activity coefficient v . Comparison of results obtained by this method with those from other techniques yields excellent agreement. Thus, the applicability of thermodynamic theory to the case of partial equilibrium in a galvanic cell with liquid junction is demonstrated. 

Does this suggest that, in theory, it should be possible to constract a galvanic cell (battery) based on any conceivable spontaneous reaction ... 

At low ambient temperatures, dry cells and other galvanic cells lose their faculty to give their nominal current output. Pyrotechnic heat sources can be employed to remedy this deficiency. Experimentally, one such system consists of cheap, easily molded, relatively cool burning pellets, inserted into metal tubes, which are immersed in the electrolyte. The pellets consist of fine iron powder and sulfur in the proportion 70/30 (theory 64/36 calc. 250 cal/g). They are easily ignited and while expanding in a semiliquid state, glow at bright red heat... 

The electrochemical theory of corrosion, as described earlier, relates corrosion to a network of short-circuited galvanic cells on the metal surface. Metal ions go into solution at anodic areas in an amount chemically equivalent to the reaction at cathodic areas. At anodic areas, the following reaction takes place ... 

Before discussing further interesting applications of solid state galvanic cells, let us first examine the thermodynamic and electrical processes which occur in these cells in the light of the general transport theory of solids. We shall then be better able to understand the applications. 

Application of the general transport theory to solid state galvanic cells Let us once again consider, as a specific example, the cell Pt/FeO, Fe3 04/Zr02(-1-Me0)/Fe304, Fe203/Pt... 

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