Data Derived from Standard Potentials

Thermodynamic Data Derived from Standard and Formal Potentials... 

The first attempt to describe the dynamics of dissociative electron transfer started with the derivation from existing thermochemical data of the standard potential for the dissociative electron transfer reaction, rx r.+x-,12 14 with application of the Butler-Volmer law for electrochemical reactions12 and of the Marcus quadratic equation for a series of homogeneous reactions.1314 Application of the Marcus-Hush model to dissociative electron transfers had little basis in electron transfer theory (the same is true for applications to proton transfer or SN2 reactions). Thus, there was no real justification for the application of the Marcus equation and the contribution of bond breaking to the intrinsic barrier was not established. 

Careful planning of the initial investigation activities is very important because this task sets the stage for future decisions and actions. Physical site characteristics, extent and intensity of contamination, cultural features, and historical background are confirmed in this project phase. Cleanup levels, potential remedial schemes, and probable costs are established with the data derived from the initial work. Regulators typically set conservative closure standards to assure public safety. Once these are established, it is difficult to modify them. Therefore, a truly representative site investigation must be completed before any remediation levels are set. 

In aqueous solution nobelium ions are most stable in the 2 oxidation state. In this oxidation state nobelium has a filled f-electron shell, 5f ", which is likely a major factor for its stability. The potential for the No(III)/No(II) couple has been calculated by Nugent et al. as 1.45 0.05 V [177]. A value of —1.4 to —1.5 V was determined by Silva and coauthors from experimental measurements [180]. David et al. have performed electrochemical amalgamation experiments for the reduction of No(II) to No(0) in aqueous acetate and citrate solutions [181]. They determined half-wave potentials of—1.709 0.006 V versus SCE in acetate and —1.780 0.004 V versus SCE in citrate. Their data was consistent with a reversible two-electron reduction process for which the data in acetate solution was taken as representative of a noncomplexing medium. The 1/2 value in acetate was converted to a value of —1.47 0.01 V versus SHE and subsequently used to derive a standard potential value of —2.49 0.06 V for the No(II)/No(0) couple. 

Out-of-laboratory measurements are undertaken across a broad range of industrial and analytical sectors for a variety of reasons in clinical and medical diagnostics for the control of chemical and petrochemical production processes and to monitor emissions and discharges to the environment. The validity of data derived from such measurements is clearly of vital importance, for example to demonstrate compliance with environmental legislation. However, it is particularly difficult to obtain valid and reliable measurements outside the laboratory. The inability to control the environment in which the measurements are made and the use of untrained operators both have potential to impact significantly on the reliability of data. The situation is made worse because of the lack of adequate QA and QC procedures, the shortage of reference materials and calibration standards, and... 

To derive a general relationship for computing equilibrium constants from standard-potential data, consider a reaction in which a species A d reacts with a species to yield and B d- The two electrode reactions are... 

The importance of conducting experiments that establishes E° for a readily available standard compound under the actual measurement conditions cannot be overstated. If this is consistently done, many of the problems that are encountered when comparing electrode potential data from different sources in the literature can be diminished. Quantitative bond energy data that are derived from electrode potentials will obviously benefit from such a standardization - note that the 0.4 V span that is found for E°(Fc) versus SGE translates to an astonishing possible error in bond energies of about 40 kj moP merely as a consequence of flawed comparisons of electrode potentials that have been measured in two different solvents ... 

The size dependency of the electrochemical oxidation of metal nanoparticles can be partially understood in the light of several different considerations. " " First, data deriving from work on small silver clusters, Agn, formed in aqueous solution via pulse radiolysis coupled with other information such as mass spectroscopic equilibrium data and Gibbs energies of sublimation of silver has led to the estimation of the standard electrode potential of the redox couple... 

It is noteworthy that the rate constants and the standard potential of the C/D couple may be derived from the experimental data playing with the concentrations of A and Z. As before, both rate constants can be derived from the absolute value of the plateau current and from its variations with the concentration ratio, Cy/C (Figure 2.24b). Once the ratio k /ki is... 

The simplest way of generating and observing aryl halide anion radicals is to use an electrochemical technique such as cyclic voltammetry. With conventional microelectrodes (diameter in the millimetre range), the anion radical can be observed by means of its reoxidation wave down to lifetimes of 10" s. Under these conditions, it is possible to convert, upon raising the scan rate, the irreversible wave observed at low scan rates into a one-electron chemically reversible wave as shown schematically in Fig. 9. Although this does not provide any structural information about RX , besides the standard potential at which it is formed, it does constitute an unambiguous proof of its existence. Under these conditions, the standard potential of the RX/RX " couple as well as the kinetics of the decay of RX-" can be derived from the electrochemical data. Peak potential shifts (Fig. 9) can also be used... 

Solubility products can be derived indirectly from standard electrode potentials and other thermochemical data, and directly from tabulated standard Gibbs energies of formation, AfG°, of the ions in aqueous solution [12]. Thus, the use of... 

The standard potential values presented above are mostly derived from thermodynamic data [3] however, where it was possible, the electrochemically measured values [2] are given. 

Moore, C. E. Ionization Potentials and Ionization Limits Derived from the Analyses of Optical Spectra, NSRDS-NBS 34 National Bureau of Standards Washington. DC, 1970, except for the data on the actinides, which are from The Chemistry ofthe Actinide Elements, Katz, J. J. Seaborg, G. T. Morss, L. R., Eds. Qiapman and Hall New York, 1986 Vol. 2. 

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