Electrode potentials values

It must be emphasised that standard electrode potential values relate to an equilibrium condition between the metal electrode and the solution. Potentials determined under, or calculated for, such conditions are often referred to as reversible electrode potentials , and it must be remembered that the Nernst equation is only strictly applicable under such conditions. 

Thus, Examples 5.1 and 5.3 illustrate that the effect of the activity coefficient on the electrode potential value (for practical purposes) is not large and decreases with decrease in concentration. 

Calculate the current density at which an alloy with 25 mol.% Cu and 75 mol.% Cd should be deposited, assuming that the deposition current density of the alloy is the sum of the deposition current density of individual metals. What is the electrode potential value at that current density [Take Z)(Cu2+) = D(Cd2+) = 5.00 x 10-10 m2 s1, u= lx 10-6 kg m-1 s-1, T = 298 K. The current... 

Electrochemical oxidation of hydroquinone was investigated on a rotating disk electrode in a solution containing 0.01 M quinone and hydroquinone in 0.5 M H2so4 at 298 K. The following values of current density at different electrode potential values and RDE rotation rates were obtained ... 

However, since one is interested primarily in comparing the potential of one electrode with that of another, the constant error involved in assuming the potential of the hydrogen electrode to be zero does not detract from the utility of the electrode potential values obtained in this manner. By making a series of such measurements using a variety of electrodes in comparison with the hydrogen electrode, an extensive list of electrode potential data may be compiled. Such a list is given in Table 11.2. 

The thermodynamic information is normally summarized in a Pourbaix diagram7. These diagrams are constructed from the relevant standard electrode potential values and equilibrium constants and show, for a given metal and as a function of pH, which is the most stable species at a particular potential and pH value. The ionic activity in solution affects the position of the boundaries between immunity, corrosion, and passivation zones. Normally ionic activity values of 10 6 are employed for boundary definition above this value corrosion is assumed to occur. Pourbaix diagrams for many metals are to be found in Ref. 7. 

Figure 6.58 Potentiodynamic polarization curve and electrode potential values at which stress-corrosion cracking appears (Jones)5...

The electrode potential value is related to the equilibrium pressure of molecular hydrogen via the equation ... 

The potential measured with an electrode in contact with a solution of its ions. Electrode potential values will predict whether a substance will be reduced or oxidized. Values are usually expressed as a reduction potential (M + —> M). A positive electrode potential would indicate that reduction is spontaneous. A negative potential for this reaction would suggest that the oxidation reaction (M —> M +) would be spontaneous. Electronegativity The tendency of an atom to pull an electron toward it in a chemical bond ... 

Frankly, it is our opinion that in this area theory and practice don t agree. Electrode potential values are of great value, and much reliance must be placed on this mahgned parameter. The dependence on electrode potentials in dialysis work is probably best emphasized by a typical example. 

The net current can be visualized as the summation of two opposing currents (cathodic and anodic). The rate of Fe reduction (conventionally expressed as cathodic current) generally increases exponentially with more negative electrode potential values and is, furthermore, a function of the concentration of... 

When the follow-up reaction leads to an electroactive product, the effects of the redox properties of the product (Z, above) on the current-potential curves also must be considered. For more than one electroactive product, the nomenclature for the model system changes from and to A and B, below, each compound having its own E (standard electrode potential) value ... 

Table 2. Electrode potential values (V) for the irreversible one-electron reduction of the linear species [M-Au-M]- in Propylene carbonate solution [25]...

Standard electrode potentials ( values) may be used to decide whether redox reactions are allowed to occur. The key point to remember here is that the halfreaction having the more positive electrode potential occurs as a reduction, while the half-reaction having the more negative electrode potential occurs as an oxidation. To help you apply this easily ... 

Before we discuss standard electrode potential, we will talk about electromotive force (emf). The electromotive force of a cell is the potential difference between the two electrodes. This can be measured using a voltmeter. The maximum voltage of a cell can be calculated using experimentally determined values called standard electrode potentials. By convention, the standard electrode potentials are usually represented in terms of reduction half-reactions for 1 molar solute concentration. The standard electrode potential values are set under ideal and standard-state conditions (latm pressure and 25°C temperature). From the MCAT point of view, you can assume that the conditions are standard, unless stated otherwise. Table 12-1 shows a list of standard electrode potentials (in aqueous solution) at 25°C. 

From Table 12-1, we can take the standard electrode potential values. The cell containing the copper electrode has a standard potential value of 0.34 V. For the other half-cell, the reaction is oxidation. Since the value given in the table is in terms of reduction half-reactions, we have to reverse the sign of the standard... 

Thus g, the cell voltage at zero current, can be estimated from the standard free energy change or from the standard electrode potentials, values of which are available in the literature (Perry and Chilton, 1976). 

For Fc-amino acid conjugates, virtually no differences were observed in the redox potentials. Sheely reported redox potentials of closely related monosubstituted Fc conjugates such as Fc-GlyOMe 37, Fc-AlaOMe 38, Fc-LeuOEt 39, and Fc-PheOEt 40 with electrode potential values in the range of 598 to 608 ( 5) mV in 0.2M TBAP/CH3CN (Scheme 5.12) [49],... 

The measurement of an electrode potential requires the use of a reference electrode [2,28] to complete the electrical circuit (Fig. 4.1.6). The SHE is chosen as the primary reference electrode and its equilibrium potential is assigned the value of zero when the activities of H" " and H2(g) are unity. Thus, the equilibrium single electrode potential values in Table 4.1.2 are relative, as they are measured with respect to the SHE, and are not absolute. 

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