Standard electrode potential IUPAC convention

Fig. 7.175. The IUPAC convention ascribes to the standard electrode potential the same sign as that experimentally observed when the electrode in question is connected to a cell with the SHE.

Thus, the IUPAC decision supports the zinc-minus-copper-plus table of standard electrode potentials. The first thing to do, therefore, when consulting a table of standard electrode potentials is to examine the E° values of the zinc and copper electrodes. If the values are -0.76 and +0.34 V, respectively, the table can be used. If, however, the values are +0.76 and -0.34 V, the convention contravenes the IUPAC decision. To use such a table, one can retain all the magnitudes of the E° values, but change all the signs of the E° values the table will then be in accord with the international convention (Table 7.23). 

In the past the electrostatic convention has often been called the European convention and the thermodynamic convention popularized by Luitmer (The Oxidation Potentials of the Elements and Their Values in Aqueous Solution Prenlicc-HBlI Englewood Cliffs. NJ, (952) the American convention. In an effort to reduce confusion, the IUPAC adopted the "Stockholm convention" in which electrode potentials refer to the electrostatic potential and end s refer to the thermodynamic quantity. Furthermore, the recommendation is that standard reduction potentials be listed as electrode potentials" to avoid the possibility of confusion over signs. 

Since in experiments such as the one we have just discussed, it is only possible to determine potential differences between two electrodes (and not the absolute potential of each half cell), it is now useful to choose a reference system to which all measured potential differences may be related. In accord with the IUPAC 1953 Stockholm convention, the standard hydrogen electrode (SHE) is commonly selected as the reference electrode to which we arbitrarily assign a zero value of electrical potential. This is equivalent to assigning (arbitrarily) a standard free energy change, ArG°, of zero at all temperatures to the half reaction ... 

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