Electrode potential calculation

At zero concentration of the potential-determining substances, the values of electrode potential calculated with Eq. (3.26) or (3.30) tend toward °°, which is physically meaningless. This implies that these equations cannot be used below a certain concentration. 

Equation (3) can be used to calculate the standard electrode potentials. Calculations based on the Bom-Haber cycle to obtain the relative stabilities of oxidation states are known as Oxidation State Diagrams . These diagrams have been found useful in clarifying inorganic chemistry (69), even though their accuracy is sometimes low. 

The electrode potentials for the two half-reactions are identical to the electrode potentials calculated in Example 19-1. That is,... 

I or each of the following half-cells, compare electrode potentials calculated from (I) concentration and (2) activity data,... 

Figure II. (a) Plots of initial current level lim against potential drcq) DE at various initial electrode potentials, reproduced from the cathodic current transients obtained from the Lii NiOz electrode, (b) variation in current with time up to 10 s by application of a potential drop df of 0.1 V at various initial electrode potentials, calculated using the simulation program with integrated circuit emphasis (SPICE) for the electric circuit of Figure 10 b), by taking the values of resistances and capacitances determined by CNLS fitting of the impedance spectra of Figure 10(a) to the electric circuit of Figure 10(b).

Organic Examples of Complete Electrode Potential Calculations... 

The electrode potential calculations, after Cq is computed, do not of course differ from those presented in Sects. 4.2.1 and 4.2.2. 

EXERCISE 20.9 Using standard electrode potentials, calculate E% at 25°C for the following cell. 

Calculating the emf from standard potentials Given standard electrode potentials, calculate the standard emf of a voltaic cell. (EXAMPLE 20.8)... 

Figure 4.24 shows the CCL polarization curves for the range of parameter between zero (no crossover) and 0.5 (large crossover). Note that Figure 4.24 shows the electrode potential calculated according to Ecath = E oi — t]ox,o. The crossover dramatically (by 300-600 mV) lowers the electrode potential at the OCP (Figure 4.24). Note that for jS between 0 and 0.2, there is a range of currents (50 to 150 mA cm ), where the polarization curve is nearly flat (Figure 4.24). This is a feature of DMFC an increase in the useful current jo lowers the crossover current jcross,o so that the sum jo + jcross.o and hence the cell potential do not change significantly.

In practice, most of the time the ionic strength of the solution in which we want to perform a redox reaction for an analytic goal is unknown. Thus, the activity coefficients are also unknown. A solution to this problem, which is a solution by default, is to mix activities and concentrations, as we did in the preceding considerations. This solution may be not very good since the medium to be analyzed can be very rich in ions and the activity values far from those of the corresponding concentrations, which are nearly always weaker. Hence, electrode potentials calculated in such a way may induce high interpretation errors. 

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