Electrochemistry standard potentials

Standard electrode potential is an important concept in electrochemistry. Standard potentials for many half-reactions have been measured or calculated. It is designated as EY and expressed in volts (V). From the values of E° one can... 

Another troublesome aspect of the reactivity ratios is the fact that they must be determined and reported as a pair. It would clearly simplify things if it were possible to specify one or two general parameters for each monomer which would correctly represent its contribution to all reactivity ratios. Combined with the analogous parameters for its comonomer, the values rj and t2 could then be evaluated. This situation parallels the standard potential of electrochemical cells which we are able to describe as the sum of potential contributions from each of the electrodes that comprise the cell. With x possible electrodes, there are x(x - l)/2 possible electrode combinations. If x = 50, there are 1225 possible cells, but these can be described by only 50 electrode potentials. A dramatic data reduction is accomplished by this device. Precisely the same proliferation of combinations exists for monomer combinations. It would simplify things if a method were available for data reduction such as that used in electrochemistry. 

In spite of the high effort focused on the carbon electrochemistry, very little is known about the electrochemical preparation of carbon itself. This challenging idea appeared in the early 1970s in connection with the cathodic reduction of poly(tetrafluoroethylene) (PTFE) and some other perfluorin-ated polymers. The standard potential of the hypothetical reduction of PTFE to elemental carbon ... 

Electrochemistry is in many aspects directly comparable to the concepts known in heterogeneous catalysis. In electrochemistry, the main driving force for the electrochemical reaction is the difference between the electrode potential and the standard potential (E — E°), also called the overpotential. Large overpotentials, however, reduce the efficiency of the electrochemical process. Electrode optimization, therefore, aims to maximize the rate constant k, which is determined by the catalytic properties of the electrode surface, to maximize the surface area A, and, by minimization of transport losses, to result in maximum concentration of the reactants. 

Standard potential of the second electron transfer more anodic than that of the first electron transfer (AE01 positive). The case in which the product Ox, generated by the chemical reaction following the first electron transfer, is more easily reduced than the original species Ox constitutes another common ECE mechanism in inorganic electrochemistry. 

The experimental kinetic data obtained with the butyl halides in DMF are shown in Fig. 13 in the form of a plot of the activation free energy, AG, against the standard potential of the aromatic anion radicals, Ep/Q. The electrochemical data are displayed in the same diagrams in the form of values of the free energies of activation at the cyclic voltammetry peak potential, E, for a 0.1 V s scan rate. Additional data have been recently obtained by pulse radiolysis for n-butyl iodide in the same solvent (Grim-shaw et al., 1988) that complete nicely the data obtained by indirect electrochemistry. In the latter case, indeed, the upper limit of obtainable rate constants was 10 m s", beyond which the overlap between the mediator wave and the direct reduction wave of n-BuI is too strong for a meaningful measurement to be carried out. This is about the lower limit of measurable... 

Electrochemistry, 20 standard potentials for, 22 Electromagnetic spectrum, 45 Electronegativity, 13, 30 Electrons, transfer of, 18 Endothermic process, 23 Energy of activation, 28 Enthalpy, 21 Entropy, 21, 23, 31 Exothermic process, 23... 

Practically in every general chemistry textbook, one can find a table presenting the Standard (Reduction) Potentials in aqueous solution at 25 °C, sometimes in two parts, indicating the reaction condition acidic solution and basic solution. In most cases, there is another table titled Standard Chemical Thermodynamic Properties (or Selected Thermodynamic Values). The former table is referred to in a chapter devoted to Electrochemistry (or Oxidation - Reduction Reactions), while a reference to the latter one can be found in a chapter dealing with Chemical Thermodynamics (or Chemical Equilibria). It is seldom indicated that the two types of tables contain redundant information since the standard potential values of a cell reaction ( n) can be calculated from the standard molar free (Gibbs) energy change (AG" for the same reaction with a simple relationship... 

In making a transition to a quantitative discussion of the electrochemistry of the alkah metals, we begin with a discussion of standard potentials. Table 1 provides a list of standard potentials for half-reactions that take the generic form found in Eq. (1)... 

While the above description has qualitative merit at an introductory level, it is important to recognize that the ground state electronic configurations apply to unassociated atoms. Ionization (oxidation) of a metal phase in a solvent produces solvated ions, and the stability of these ions is an important influence on the value of the standard potential. Descriptions of alkali metal electrochemistry that are more informative than descriptions based on ground state electronic configurations and periodicity can be obtained by inspection of simple thermodynamic balance sheets. One scheme for assigning the contributions to the oxidation process in solutions is shown in Fig. 1. 

The standard potentials listed in Table 1 are all at 298.15 K. Given that not all electrochemistry is done at 298.15 K, it is useful to consider the temperature dependence of the standard potentials for the alkali metals. The temperature dependence can be obtained from the change in entropy, which is given by Eq. (5). 

First of all, the important role of platinum as the metal part of the standard hydrogen electrode (SHE), which is the primary standard in electrochemistry should be mentioned. The standard potential of an electrode reaction (standard electrode potential) is defined as the value of the standard potential of a cell reaction when that involves the oxidation of molecular hydrogen to solvated (hydrated) protons (hydrogen ions) ... 

These reactions are solid-state insertion electrochemical processes with coupled electron and ion transfers. Figure 4 includes the standard potential of hex-acyanoferrate in aqueous solution. It is rather surprising that the data for the solid-state insertion electrochemistry and... 

Although the entire discussion of electrochemistry thus far has been in terms of aqueous solutions, the same principles apply equaly well to nonaqueous solvents. As a result of differences in solvation energies, electrode potentials may vary considerably from those found in aqueous solution. In addition the oxidation and reduction potentials characteristic of the solvent vary with the chemical behavior of the solvent. as a result of these two effects, it is often possible to carry out reactions in a nonaqueous solvent that would be impossible in water. For example, both sodium and beryllium are too reactive to be electroplated from aqueous solution, but beryllium can be electroplated from liquid ammonia and sodium from solutions in pyridine. 0 Unfortunately, the thermodynamic data necessary to construct complete tables of standard potential values are lacking for most solvents other than water. Jolly 1 has compiled such a table for liquid ammonia. The hydrogen electrode is used as the reference point to establish the scale as in water ... 

Note that subscripts c and a have been added to differentiate the cathodic and anodic mass transport limiting currents, respectively. These relationships are important in general electrochemistry experiments, because they allow the voltam-metric determination of standard potentials. 

P. Longhi, T. Mussini, R. Orsenigo and S. Rondinini, Redetermination of the standard potential of the mercuric oxide electrode at temperatures between 283 and 363 K and the solubility product constant of mercuric hydroxide , Journal of Applied Electrochemistry, 17,1987, pp 505-514. 

The electrochemistry was performed on the neat ionic liquid. In such a set-up, with no recognised background electrolyte or redox standard, the potential vs. the platinum pseudo-reference is difficult to compare with standard potentials, however, in such unusual conditions it is the qualitative nature of the electrochemistry that is important. ... 

As shown in Equation (19), it is conventional for Nernst equations to represent the sum of E° and the logarithmic term, rather than the difference. Consequently, in the activity quotient, the activity of the oxidized form of the electroactive species has to be written as the numerator. Standard potentials of individual electrode reactions are conveniently available in textbooks of physical chemistry and electrochemistry, and in relevant handbooks. A small selection is presented in Table 3.1.3. 

Refs. [i] Parsons R (1974) Pure Appl Chem 37 503 [ii] Inzelt G (2006) Standard potentials. In BardAJ, Stratmann M, ScholzF, Pickett CJ (eds) Encyclopedia of electrochemistry, vol. 7a, Wiley-VCH, Weinheim... 

Refs. [i] Sawyer D, Sobkowiak A, Roberts ]L Jr (1995) Electrochemistry for chemists, 2nd edn. Wiley Interscience, New York [ii] Inzelt G (2006) Standard potentials (chap. 1). Platinum (chap. 17.3). In Bard A), Stratmann M, ScholzP, Pickett C (eds) Inorganic chemistry. Encyclopedia of electrochemistry, vot 7a. Wiley-VCH, Weinheim [Hi] Kahlert H (2002) Reference electrodes. In Scholz P (ed) Electroanalytical methods. Springer, Berlin, pp 263-264... 

Refs. [i] Bard AJ, Parsons R, Jordan J(1985) Standard potentials in aqueous solution. Marcel Dekker, New York [ii] Hamnett A (1999), Mechanism of methanol electro-oxidation. In Wieckowski A (ed) Interfacial electrochemistry. Wiley, New York [iii] Hamnett A (2003) Direct methanolfuel cells (DMFC). Ire Vielstich W, Lamm A, Gasteiger H (eds) Handbook of fuel cells fundamentals, technology, applications, vol. 1. Wiley, Chichester, chap 18, pp 305-322... 

Refs. [i] Latimer WM (1952) Oxidation potentials. Prentice-Hall, Englewood Cliffs [ii] Parsons R (1985) Redox potentials in aqueous solutions a selective and critical source book. Marcel Dekker, New York [Hi] Bard AJ, Parsons R, Jordan J (1985) Standard potentials in aqueous solutions. Marcel Dekker, New York [iv] Antelman MS, Harris FJ (eds) (1982) The encyclopedia of chemical electrode potentials. Plenum Press, New York [v] Pourhaix M (1963) Atlas d equilibres electrochemiques. Gauthier-Villars, Paris [vi] Bratsch SG (1989) J Phys Chem Ref Data 18 1 [vii] InzeltG (2006) Standard potentials. In Bard AJ, Stratmann M, Scholz F, Pickett CJ (eds) Inorganic electrochemistry. Encyclopedia of electrochemistry, vol. 7a. Wiley-VCH, Weinheim, chap 1 [viii] Stanbury DM (1989) In Sykes AG (ed) Advances in inorganic chemistry, vol. 33. Academic Press, New York, p 69 [ix] Wayner D, Parker VD (1993) Acc Chem Res 26 287... 

A. J. Bard, R. Parsons, and J. Jordan, Standard Potentials in Aqueous Solutions, in Monographs in Electroanalytical Chemistry and Electrochemistry, Marcel Dekker, New York, 1985. 

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