Presentation in predominance diagrams

How such a EH-pH diagram can be determined analytically is explained below using the example of the Fe-02-H20 diagram shown in Fig. 15 left. In each Es-pH diagram the occurrence of the aqueous species is limited by the stability field of water. Above this field H20 converts to elementary oxygen, below this field to elementary hydrogen (also see Fig. 16). 

The diagram s vertical boundaries (Fig. 15, number 1-5) are reactions that describe a dissolution in water (hydrolysis) independent of the EH value. The boundaries of the respective predominance fields are calculated via the equilibrium constants for the conversion of the species at each side of the boundary line into each other. 

In contrast, the conversion of Fe3+ into Fe2+ (Fig. 15, number 6), is a pure redox reaction, independent of the pH-value (horizontal boundary). It is calculated after Eq. 58  

For the calculation of the boundary line the activity of both species is equal, i.e. red = ox. Thus the argument of the logarithm is 1 and the logarithm is 0, i.e. 

The boundaries running diagonally display species transformations, which depend on pH and EH. After Eq. 59 

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