Redox thermodynamics for oxygen species

Redox Thermodynamics for Oxygen Species Electrode material effects... 

The reaction thermodynamics for oxygen species are influenced by the solution matrix and its acidity. Thus, the redox thermodynamics of O2 are directly dependent upon hydronium ion activity,... 

Fig. 2. Thermodynamics of the reduction of oxygen species Potential diagram at pH 7. Figures are apparent standard redox potentials versus NHE, at pH 7. Figures used for the alkyl peroxide species at the top of the diagram are approximations derived from computations by Koppenol [19]. An upper value for the ROO /ROOH redox couple would be 1.1 V, i.e. the value derived from the trichloromethyl peroxyl radical, the strongest oxidant known among peroxyl radicals. See the discussion in the text. Note (see a) A aq -0.16 V (relative to 1 M 02) is a better reference than —0.33 V for the reversible...

The problems at lower temperatures happen because reactions are slow and systems are often far out of equilibrium. (The thermodynamically stable state for all the flora and fauna in any well-aerated lake should be H2O and CO2, for example). Reaction rates increase exponentially with temperature however, and at temperatures of 350°C or higher, even reactions involving molecular oxygen can equilibrate in several days time. This is fortunate, because free energy data are sparse for aqueous species at elevated temperatures and it becomes difficult to measure or calculate Eh much above 100°C. Instead, we can use other reactions between redox-sensitive species to calculate redox-related parameters at higher temperatures. This is the subject of the following section. 

Owing to the allotropic forms of oxygen, to its various redox states, and related chemical species that are thermodynamically stable or exist for kinetic reasons, a lot of redox reactions are usually described. However, many of them are not really important for the common works, particularly for those in solutions consequently, only some of them have been described here. The publications cited earlier can be searched for data useful for the calculation of Gibbs energy or potentials of particular reactions. 

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