Standard Electrode Potentials

Figure 10.5 shows the M/Mz+ half-cell combined with the hydrogen half-cell which, in addition, is the SHE. To establish an electrochemical database, the metal M must be pure and the Mz+ activity must be unity. If unit activity of Mz+ does not fall in the Henry's law region, the concentration cMZ+ which renders aMZ+ = 1 is determined by the same method applied above for H+. The M/Mz+ half-cell with these restrictions is termed a standard electrode and the measured EMF, s°, in Eq (10.26) is the standard electrode potential of the M/Mz+ half-cell reaction. This corresponds to the overall reaction with all species in their standard states, so Eq (10.24) becomes

The database for aqueous electrochemistry consists of standard electrode potentials for a large number of half-cell reactions. Since most aqueous systems are at room temperature, a single table at 25oC suffices to accommodate the entire database. An abridged table of standard electrode potentials is given in Table 10.1. A more extensive tabulation can be found in Ref. 1

According to Eq (10.30), the sign of s° is opposite that of the standard chemical-potential change of the overall cell reaction. By convention, the overall cell reaction is written with the oxidized portion of the couple written on the right hand side, as it appears in Eq (10.21). Or, the half-cell reaction for the couple is written with the electrons on the right. With this convention, couples involving a very reactive metal will tend to exhibit negative values of (because the ions are very stable in solution) and conversely, positive s°.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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