Some galvanic cells without liquid junction

A third possible convention is due to Gibbs. Here the emphasis is on the cell itself, rather than the depiction of the cell. The emf of the cell is always positive and the difference between the standard half-cell potentials is taken to yield positive values. Then 

Throughout this discussion we have considered cells in which the electrolytic solution is an aqueous solution. The same methods can be used to define standard half-cell potentials in any solvent system. However, it is important to remember that when the reference state is defined as the infinitely dilute solution of a solute in a particular solvent, the standard state depends upon that solvent. The values so obtained are not interchangeable between the different solvent systems. Only if the standard states could all be defined independently of the solvent would the values be applicable to all solvent systems. 

11 Some galvanic cells without liquid junction 

Values of activity coefficients can also be obtained from the emf of cells. For the purposes of discussion we continue with the cell 

We cannot determine values of the activity coefficients of the individual ions, but by definition of the mean activity coefficients (Eq. (11.182)), we have 

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The Variation of the Standard Potentials of Some Electrodes with the Temperature. In a number of cases the standard potentials of galvanic cells without liquid junctions have been determined over a range of temperatures. From these determinations it has been possible to prepare Table V, which gives the standard potentials of a number of electrodes at intervals of 12.5° from 0° to 50°. Some slight adjustments, of the order of 0.2 millivolt, of the original data have been necessary to bring the figures into accord with the Ho values at 25° adopted in this book. A more complete table of standard potentials of the elements at 25° will be found at the end of Chapter 14. 

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