Chemical equilibria thermodynamics Nernst equation

In spite of the above justification for the kinetic approach to the estimate of l, this has a number of drawbacks. First of all, there is no point in using a kinetic approach to determine a thermodynamic equilibrium quantity such as l. The justification of the validity ofEqs. (42) and (45) by the resulting equilibrium condition of Eq. (46) is far from rigorous, just as is the justification of the empirical Butler-Volmer equation by the thermodynamic Nernst equation. Moreover, the kinetic expressions of Eq. (41) involve a number of arbitrary assumptions. Thus, considering the adsorption step of Eq. (38a) in quasi-equilibrium under kinetic conditions cannot be taken for granted a heterogeneous chemical step, such as a deformation of the solvation shell of the... 

Reversibility — This concept is used in several ways. We may speak of chemical reversibility when the same reaction (e.g., -> cell reaction) can take place in both directions. Thermodynamic reversibility means that an infinitesimal reversal of a driving force causes the process to reverse its direction. The reaction proceeds through a series of equilibrium states, however, such a path would require an infinite length of time. The electrochemical reversibility is a practical concept. In short, it means that the -> Nernst equation can be applied also when the actual electrode potential (E) is higher (anodic reaction) or lower (cathodic reaction) than the - equilibrium potential (Ee), E > Ee. Therefore, such a process is called a reversible or nernstian reaction (reversible or nerns-tian system, behavior). It is the case when the - activation energy is small, consequently the -> standard rate constants (ks) and the -> exchange current density (jo) are high. 

As with any chemical process, it is necessary to consider both the thermodynamics and kinetics of the electron transfer process. If the cell potential is monitored while allowing no current to flow through the cell, the potential of the working electrode will eventually reach a steady state value indicating that the cell is in equilibrium. The potential of the WE is then given by the Nernst equation... 

As with any chemical process, it is logical first to consider the thermodynamics. Suppose the potential of the working electrode vs. the reference electrode is monitored while no current is allowed to flow. Under these circumstances no chemical change can occur at the surface and the solution composition will remain unchanged and uniform. The working electrode will take up its equilibrium (or reversible) potential E, which may also be calculated from the Nernst equation ... 

The pictorial model outlined leads us to expect that when the metal and solution are at equilibrium this will correspond to an exact matching of the energy levels in the solution with the Fermi level. When this point is reached there will be a difference of charge and hence of potential between the metal and solution phases. This is the basic origin of the Nernst equation outlined earlier and which we will shortly derive in more general terms once we have briefly reviewed how equilibrium is described by the science of chemical thermodynamics. 

Walther Hermann Nemst (1864-1941) was a German physical chemist who is known for his theories behind the calculation of chemical affinity as embodied in the third law of thermodynamics, for which he won the 1920 Nobel Prize in Chemistry. Nemst also made fundamental contributions to the theory of electrolyte solutions. He is most known for developing the Nernst equation, one of the most fundamental equations of equilibrium electrochemistry. 

He said that the vap. press, curve of liquid nitric oxide is somewhat anomalous, and this is attributed to polymerization of the molecules at low temp. The fact that the vapour density at atmospheric press, is quite normal at these temp, indicates, however, that the dissociation of the polymerized mols. is practically complete at this pressure. The high density of the liquid at its b.p., 1 -269, is cited as evidence in support of the view that the liquid mols. are associated. W. Nernst s value for the chemical constant is about 3-7 J. R. Partington s, 1-263 F. A. Hen-glein, and A. Langen, 0-92 and A. Eucken and co-workers gave 0-03 for the integration constant of the thermodynamic vap. press, equation and A. Eucken and F. Fried, 0-95 for the constant in the equilibrium equation for 2NO=N2-j-02. 

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