Nernst vapor-pressure equation

The temperature was 25°C (the standard condition) and atmospheric pressure was 751.0 Torr. Because the vapor pressure of water is 23.8 Torr at 25°C, PHi n the cell was 751.0 - 23.8 = 727.2 Torr. The Nernst equation for the cell, including activity coefficients, is derived as follows ... 

We can estimate the voltage difference between using saturated air and O2 based on the Nernst equation at 57°C, where the saturated vapor pressure is 0.17 bars. With pure O2, its partial pressure is 0.83 bars, and with air having 21% O2, the O2 partial pressure is 0.17 bars (0.83 x 0.21). Therefore,... 

Nernst shows that equation (6a) aind (6d) are equivalent if the lowering of the vapor pressure by a binary electrolyte is twice as great as that produced by the same concentration of a nonelectrolyte, and notes that it is "mcht uninteressant that this is in agreement with Arrheniuses h Tpothesis of complete ionic dissociation. However, Nernst adds, Helmholtz s thermodynamic treatment gives no guide as to the location or locations of the potential diffc rences which combine to produce the cell emf, whereas his summation is explicit and furthermore provides a mechanistic reason f(.rr the equivalence of electrical and chemical energy. 

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