Redox potential combination

L. B. Kriksunov, C. Liu and D.D. Macdonald. Oxygen, Hydrogen and Redox Potential Combination Sensors for Supercritical Aqueous Systems, Proc. 1 IntT. Workshop Supercritical Water Oxidation, Amelia Island Plantation, FL, February, 1995. 

The diagram gives regions of existence, i.e. for a particular combination of pH and redox potential it can be predicted whether it is thennodynamically favourable for iron to be inert (stable) (region A), to actively dissolve (region B) or to fonn an oxide layer (region C). 

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

In general, thermodynamic stability of a mixed-valence dinuclear complex, which is denoted as a combination of reduced (Red) and oxidized (Ox) sites, Red-Ox, is exhibited as a difference in redox potentials AE° = E°(Ox-Ox/Red-Ox) - °(Red-Ox/Red -Red). This difference is related to the comproportionation constant, Kc, defined in Eq. (1) ... 

Redox Potentials enj of a Linearly Combined Multi-Redox System Based on the Neighboring-Site Interaction Model... 

A combination of cat. Ybt and A1 is effective for the photo-induced catalytic hydrogenative debromination of alkyl bromide (Scheme 28) [69]. The ytterbium catalyst forms a reversible redox cycle in the presence of Al. In both vanadium- and ytterbium-catalyzed reactions, the multi-component redox systems are achieved by an appropriate combination of a catalyst and a co-reductant as described in the pinacol coupling, which is mostly dependent on their redox potentials. 

Thermochemistry. Chen et al.168 combined the Kohn-Sham formalism with finite difference calculations of the reaction field potential. The effect of mobile ions into on the reaction field potential Poisson-Boltzman equation. The authors used the DFT(B88/P86)/SCRF method to study solvation energies, dipole moments of solvated molecules, and absolute pKa values for a variety of small organic molecules. The list of molecules studied with this approach was subsequently extended182. A simplified version, where the reaction field was calculated only at the end of the SCF cycle, was applied to study redox potentials of several iron-sulphur clusters181. 

Li, G.H. Zhang, X.D. Cui, Q., Free energy perturbation calculations with combined QM/MM. Potential complications, simplifications, and applications to redox potential calculations, J. Phys. Chem. B 2003,107, 8643-8653. 

For the prevention of nuisance therefore there are two possibilities. First, the formation or release of odorous chemical species can be discouraged. In practice this usually means the prevention of reducing conditions (negative redox potential) and possibly the prior removal of certain key compounds. Second, the time of contact between the sludge/ slurry and the air can be reduced, for example by ploughing in or sub-surface injection, and the act of spreading can be timed to coincide with favourable atmospheric conditions. These two approaches can of course be used in combination. 

Table XVI shows a selection of stability constants and redox potentials for iron(II) and iron(III) complexes. This Table covers a wide range of the latter, showing how the relative stabilities of the iron(II) and iron(III) complexes are refiected in. B (Fe /Fe ) values. A more detailed illustration is provided by the complexes of a series of linear hexadentate hydroxypyridinonate and catecholate ligands, where again high stabilities for the respective iron(III) complexes are refiected in markedly negative redox potentials (213). The combination of the high stabilities of iron(III) complexes of hydrox5rpyridinones, as of hydroxamates, catecholates, and siderophores, and the low stabilities of their iron(II) analogues is also apparent in Fig. 8. Here redox potentials for hydroxypyranonate and hydroxypyridinonate complexes of iron are placed in the overall context of redox potentials for iron(III)/iron(II) couples. The -(Fe /Fe ) range for e.g., water, cyanide, edta, 2,2 -bipyridyl, and (substituted) 1,10-phenanthrolines is...

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