Nernsts Theory

Butler, J. A. V., The kinetic interpretation of the Nernst theory of electromotive force, Trans. Faraday Soc., 19, 729 (1924). 

W. Nernst. Theorie der Reaktions-geschwindigkeit in heterogenen Systemen. Z. Phys. Chem. 1904, 47, 52-55. 

A rational deduction of elemental abundance from solar and stellar spectra had to be based on quantum theory, and the necessary foundation was laid with the Indian physicist Meghnad Saha s theory of 1920. Saha, who as part of his postdoctoral work had stayed with Nernst in Berlin, combined Bohr s quantum theory of atoms with statistical thermodynamics and chemical equilibrium theory. Making an analogy between the thermal dissociation of molecules and the ionization of atoms, he carried the van t Hoff-Nernst theory of reaction-isochores over from the laboratory to the stars. Although his work clearly belonged to astrophysics, and not chemistry, it relied heavily on theoretical methods introduced by and associated with physical chemistry. This influence from physical chemistry, and probably from his stay with Nernst, is clear from his 1920 paper where he described ionization as a sort of chemical reaction, in which we have to substitute ionization for chemical decomposition. [81] The influence was even more evident in a second paper of 1922 where he extended his analysis. [82]... 

The P s are now permeability coefficients and are related to the mobilities of the ions as in the original Nernst theory. The subscripts in and out refer to the concentrations of the ions inside and outside the membrane and the P s describe diffusion coefficients, mobilities, and the membrane thickness, but, in the Hodgkin-Huxley theory, were used as adjustable parameters. 

Before the Nernst theory was proposed, H. Goldschmidt1 had already employed this idea for studying the relation between reaction velocity and concentration of aromatic nitro-bodies. 

The contradiction is only an apparent one, and the difference between the theories lies in the hypotheses. The measurement of the speeds of reaction depends upon the conditions of the experiment. If the reaction between two components of reaction actually takes place instantaneously, we can vary the time of reaction entirely at will by the period of time during which we add one of the components. If the latter is used up with immeasurable rapidity, the measured velocity of reaction must naturally always remain proportional to the added quantity of the reaction components. The Nernst theory is based on relations in which this subsequent delivery is effected only by the diffusion, the reacting agent furnished by the current being... 

If experiment shows that the exponent must be 2/3, it must be assumed that v = a d, etc. In any case 6 is not independent of D as the Nernst theory originally assumed. 

That the rate-controlling process might change with conditions has been realized since the early days of the Nernst theory. For example at high stirring speeds the surface process might be slower than convective transport. In 1909 Wilderman (32) reported that benzoic acid reached a maximum dissolution rate but examination of his data shows that the... 

W. Nernst Theorie der Reaktions ges chwindigkeit in heterogenen Systemem, Z. Phys. Chem., 47 52 (1904). 

Near the end of the last century, Nernst " proposed the basic concept of ionic movement in an electrolyte system. In an electrolyte system, ions are acted upon by two kinds of forces relevant to our discussion the coulombic force and the osmotic force, which is essentially equal to the force of diffusion due to the ionic concentration difference. According to the Nernst theory, the liquid junction potential exhibited at the interface of two electrolyte solution phases with different ionic concentrations arises essentially from the difference in ionic mobilities across the liquid junction. 

The diffusion potential theory has its origins in the Nernst theory formulated to describe the liquid junction potential developed at the interface of two electrolytes with different ionic concentrations and ionic mobilities. For two univalent ionic solutions the liquid junction potential is given by... 

Works by Karpfen and Randles [48], Boenhoffer, Kahlweit, and Strehlow [49-54, 3], Dupeyrat [55-57], Gavach and coworkers [58-61], Joos and Verburgh [62-63], as well as by Koczorowski et al. [64-67] allowed quantitative verification of the Nernst theory and practical application of liquid cells for various physicochemical purposes. In this research, in particular in Refs. [48, 52, 64], strictly reproducible experimental reference systems for the determination of distribution potentials were defined (see Sect. 4). 

The Nernst theory makes the questionable assumption of a constant geometry for diffusion. A more accurate treatment, due to Nielsen ( ), yields the relationship ... 

First we will consider the Nernst theory as represented by Eq. (10). 

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