Oxygen-H2O Redox Couple

In natural systems, oxygen reduction occurs at the upper end of the Eh scale. 

The Nemst equation (Equation 4.65, Chapter 4) can be used to describe the relationship between oxygen content and Eh  

FIGURE 6.2 Eh-pH phase diagram for oxygen-water redox couple (Bolin et al., 1979). 

When the activity of pure water is unity and = 1 atm, then we obtain 

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