Nernst potential equation

Single electrode potentials have been measured at Sn02 anodes and ITO cathodes for solutions in 50 v/v % aqueous CH3CN,. OIM in H2SO4, in which the photostationary ratio of TH to TH4 varied by a factor of more than 10 and the Fe(III) Fe(II) ratio varied by a factor of approximately six (J). The potential at the SnO anode paralleled the potential calculated for the TH" TH42 couple from known compositions with the aid of the Nernst potential equation. Measured values were, however. 

Given that AG° for the synthesis of ATP from ADP and phosphate is 30.5 kJ mol , and assnming that two protons are translocated by the mitochondrial ATP synthase per molecnle of ATP synthesized, nse the Nernst potential equation to calcnlate the minimum value of Ap necessary for synthesis of ATP. (Hint Ap has nnits of kJ mop how can this be converted to nnits of mV to give Ap as proton-motive force Apl)... 

Interaction of the analyte with the membrane results in a membrane potential if there is a difference in the analyte s concentration on opposite sides of the membrane. One side of the membrane is in contact with an internal solution containing a fixed concentration of analyte, while the other side of the membrane is in contact with the sample. Current is carried through the membrane by the movement of either the analyte or an ion already present in the membrane s matrix. The membrane potential is given by a Nernst-like equation... 

Building on initial work [47], the main focus of SECM in the study of ET at ITIES has been to identify and understand the potential-dependence of ET rates. In these studies, the potential drop across an ITIES has been controlled by varying the concentration of potential-determining ions in the two phases. The potential drop across an ITIES follows the Nernst-Donnan equation [74,75],... 

As demonstrated in the preceding section, an electric potential gradient is formed in electrolyte solutions as a result of diffusion alone. Let us assume that no electric current passes through the solution and convection is absent. The Nernst-Planck equation (2.5.24) then has the form ... 

The membrane potential expressed by Eqs (6.1.3) and (6.1.4) is termed the Nernst membrane potential as it originates from the analogous ideas as the Nernst equation of the electrode potential (p. 165) and the equation of the Nernst potential at ITIES (Eq. (3.3.50)). 

Ion transport across membranes can be evaluated by using mucosal and serosal electrodes to read transepithelial current (I) and potential difference OP). With these parameters, equivalent circuit analysis can be utilized to account for the relative contributions of transcellular and paracellular pathways. Ionic flux (J) is defined by the Nernst-Planck equation,... 

The program reports in its output the resulting redox potential for each redox couple, as calculated from the Nernst equation. The Nernst potentials, arranged in decreasing order, are... 

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. 

The ideas of Overton are reflected in the classical solubility-diffusion model for transmembrane transport. In this model [125,126], the cell membrane and other membranes within the cell are considered as homogeneous phases with sharp boundaries. Transport phenomena are described by Fick s first law of diffusion, or, in the case of ion transport and a finite membrane potential, by the Nernst-Planck equation (see Chapter 3 of this volume). The driving force of the flux is the gradient of the (electro)chemical potential across the membrane. In the absence of electric fields, the chemical potential gradient is reduced to a concentration gradient. Since the membrane is assumed to be homogeneous, the... 

If there is a net transport of charge across the membrane, the membrane potential will influence the solute transfer and also be affected by it, complicating the data treatment. The starting point for most descriptions of the internalisation flux of permeant ions, i, is the one-dimensional Nernst-Planck equation (cf. equation (10)) that combines a concentration gradient with the corresponding electric potential gradient [270] ... 

Other resolutions of the Poisson Nernst Planck equations (i.e. using various simplifying assumptions) have been proposed that couple the adsorption, desorption and permeation of ions through a membrane (e.g. [273,274]) as might be observed for a carrier-mediated transport. For example, for a symmetrical membrane (identical electrolyte on both sides of the membrane) and variation in the electrical potential profile given by i//m, /int can be estimated from ... 

Nernst Equation for Concentration Dependence of RedOx Potential. Equation (5.9) applied to the general RedOx electrode (5.16) yields... 

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... 

Similar statements can be made about holes. They, too, have to be transported to the interface to be available for the receipt of electrons there. These matters all come under the influence of the Nernst-Planck equation, which is dealt with in (Section 4.4.15). There it is shown that a charged particle can move under two influences. The one is the concentration gradient, so here one is back with Fick s law (Section 4.2.2). On the other hand, as the particles are changed, they will be influenced by the electric field, the gradient of the potential-distance relation inside the semiconductor. Electrons that feel a concentration gradient near the interface, encouraging them to move from the interior of the semiconductor to the surface, get seized by the electric field inside the semiconductor and accelerated further to the interface. 

The terms /qRp and E ere are independent of the concentration q of analyte i and, as described previously, the use of saturated KC1 minimises the value of the E term. Therefore, the potential difference measured is almost solely due to the membrane and is related to the activity of the ionic species under analysis in the sample solution by the following Nernst-type equation ... 

Unlike anions that specifically adsorb at electrodes, cations normally do not lose their solvation shell due to their smaller size and are electrostatically adsorbed at electrodes at potentials negative to the pzc. However, depending on the affinity with the foreign substrate, cations can be reduced to a lower oxidation state or even discharged completely to the corresponding metal atom at the sub-monolayer or monolayer level at potentials positive to the equilibrium Nernst potential for bulk deposition. This deposition of metal atoms on foreign metal electrodes at potential positive to that predicted by the Nernst equation for bulk deposition has been called underpotential deposition and has been extensively investigated in recent years. Detailed discussion of the... 

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... 

Values of E° by definition refer to conditions under which all species are in their standard states at 298 K. For non-standard conditions the electrode potential, E, of a redox reaction is given by the familiar Nernst expression (equation 24), where... 

R. Schlogl (144) obtained, through his general integration of the Nernst-Planck equations, also values for the diffusion potential. The approximations in the calculations are the same as those used for the fluxes (cf. 3.4). 

This interface is also known as the perm-selective interface (Fig. 6.1a). It is found in ion-selective sensors, such as ion-selective electrodes and ion-selective field-effect transistors. It is the site of the Nernst potential, which we now derive from the thermodynamic point of view. Because the zero-current axis in Fig. 5.1 represents the electrochemical cell at equilibrium, the partitioning of charged species between the two phases is described by the Gibbs equation (A.20), from which it follows that the electrochemical potential of the species i in the sample phase (S) and in the electrode phase (m) must be equal. 

The Nernst-Planck equation constitutes the starting point for the electrotransport models [55-57], The overall flux of the ionic species i (/,) comprises the diffusion term driven by the chemical potential gradient (dc,/dx) and the electric transference term due to the electrical potential gradient (d /dx) ... 

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