Nernst’s equation

Since the absolute and the conventional electrode potentials differ only by an additive constant, the absolute potential depends on the concentration of the reactants through the familiar Nernst s equation. This dependence is implicitly contained in Eq. (2.6) the real Gibbs energies of solvation contain an entropic term, which depends on the concentration of the species in the solution. 

If the electron-transfer reaction were infinitely fast, the overpotential would be given by Nernst s equation in the form ... 

According to Nernst s equation, there should be a linear relationship between the equilibrium potential of the metal/metal-ion electrode (M/M ) and the logarithm of the concentration of ions [Eq. (5.13)]. This linear relationship was observed experimentally for a low concentration of the solute MA (e.g., 0.01 mol/L and lower). For higher concentrations, a deviation from linearity was observed (see, e.g.. Fig. 5.12). The deviation from linearity is due to ion-ion interactions. In the example in Figure 5.12, the ion-ion interactions include interaction of the hydrated Ag ions with one... 

Nernst s equation, 857, 1057, 1058, 1060, 1062 1066 1255. 1351 diffusion layer, 1233 electrochemical potential, 1064 equilibrium potential difference. 1061 importance, 1064... 

Nernst s equation is timeless. Theories of the mechanism of electrode reaction may change as a consequence of the availability of new experimental results and new ideas for interpreting them. However, thermodynamic treatments involve no molecular assumptions. They depend only on the validity of the two great generalizations of experience that constitute the first two laws of thermodynamics. Therefore, conclusions reached by applying them are not expected to change. 

Notice that, although relationship (74) superficially resembles the Nernst equation, it differs from this equation in two important respects. First, it relates to the inactive ion. Second, it gives a potential difference inside the solution, not across the electrodes as shown in Fig. 22. If the electrode reactions are sufficiently rapid so that Nernst s equation is obeyed (which is not necessarily the case), the actual interelectrode potential difference would be... 

The concentrations are then used instead of the activities in various-thermodynamic expressions (e.g., the equilibrium law, and Nernst s equation for the e.m.f.). Some physical chemists are suspicious of this method. However, it is just as thermodynamic as the traditional one, the only difference being that another activity scale is used. 

During the operation of the Daniell cell the concentration (activity) of zinc ions is increased and the activity of the cupric ions is decreased. In this way its electromotive force diminishes, until finally it will drop to zero. By substituting this condition (E — 0) into the already mentioned Nernst s equation the value of the ratio aZn++/acu++ can be calculated at which the cell is completely inactive. The activity ratio mentioned at the same time expresses the equilibrium constant of the reaction taking place in the Daniell cell ... 

From Nernst s equation related to individual equilibrium potentials we may deduce that the oxidizing power of hydrogen peroxide, which is higher with a more positive reduction potential of the system (lb), grows with increasing concentration of the hydrogen ions in the solution. On the other hand the... 

Precisely symmetrical models of aqueous electrode interfaces are often shown for educational purposes. Polar water molecules and positive ions are assembled in a repetitive array. In reality the array would be interrupted by impurities and irregularities, all thermally agitated. The precise achievement of a potential difference V , corresponding to Nernst s equation (4.1), would require microscopically uniform conditions at the interface between electrode and electrolyte, so as to avoid local variations of potential difference and circulating currents in the electrode. 

Gibbs potential, the units of which are related to the electrical potential by Nernst s equation ... 

Lederer used a formula analogous to Nernst s equation for the equilibrium constant of a chemical reaction ... 

Herz foimd that the ratios of the densities of liquid and vapour at equal fractions of the critical temperature are fairly constant in homologous series, but may vary from 7 to 12 for different classes of substances. He also found that Nernst s equation (33) ... 

In (a) the linear term in T does not appear, since the variation of the specific heats is not taken into account. The terms in log T differ by a constant factor, since the specific heats of the gases were calculated from the kinetic theory in (a), while in (6) Nernst s formula c, = 3 -5 -f x 1 -5 -f aT was used. The constants of the two equations are therefore different. As both equations are equally well confirmed by experiment, we might at first sight suppose them to have equal theoretical significance. Equation (6) is, however, much the more valuable of the two, as the numerical values of its constants can be calculated from measurements with the pure substances which take part in the reaction, while in (a) a determination of the equilibrium is necessary. Nernst s equation (6) is superior to the older equation, in that it enables... 

Outside the cells, the dried gas is pressurized by multistage reciprocating or screw compressors. But the pressure can also be generated in the electrolyzer itself, remembering that after Nernst s equation the decomposition voltage for the reaction H2O —x 112 + I/2O2 amounts to Ed = 1.23 + 0.045 lgp (at standard temperature). This means an additional cell voltage of 45 mV per decade of pressure is needed. By the way, if within... 

This feature of the FET is transformed into high sensitivity in the ISFET. That is, in order to go over from the FET to the ISFET it is sufficient to replace the insulating layer by an ion-selective membrane permeable only to one sort of iont and the metal gate by an electrolyte solution, which contains a reference electrode needed to short circuit the electric circuit (Fig. 19b). The potential, which develops across the membrane in the presence in the solution of that sort of ions for which the membrane is selectively permeable, acts here as an external voltage on the gate. This potential can be determined from Nernst s equation [cf. Eq. (4)]... 

The EMF of the cell depends on the partial pressure of CO and is good agreement with the values calculated from Nernst s equation because the activity of NajO is constant in NASICON or P-Al Oj. Furthermore, the simplification and the miniaturization were accomplished by using a solid reference electrode. 

Again, we call A

basic values. According to Eq. (22.16), Aq> increases with the concentration of metal ions The more craicentrated the solution, the higher the potential (Me) compared to (S). This equation, which describes the concentration dependency of A

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Nernst s Equation In closing, we will talk about the concentration dependency of the redox potential. We obtain the following relation for a simple redox pair Rd Ox + VgC by inserting the // (Rd/Ox) defining equation into Eq. (23.3) ... 

Now proceed by dividing (9-5) by -z F and replacing the ratio -GIzF by E. This is the so-called Nernst s equation, after the German physical chemist Walter Nernst ... 

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