Electrochemistry equilibrium constants, measuring

Electrochemistry is one of the main methods used to determine equilibrium constants that are either very large or very small. To measure the equilibrium constant for the reaction of Fe(CN) 4 with Na2Cr207, the following cell was built ... 

The kinetic measurements must be accompanied by conductivity measurements, and the electrochemistry, i.e., the composition of the ionic population, and any equilibrium constants such as KD must be established by measurements during and after polymerisation and with model compounds, and secondary effects, such as that of m on Kd, must be investigated. 

Electroanalytical chemistry has been defined as the application of electrochemistry to analytical chemistry. For the determination of the composition of samples, the three most fundamental measurements in electroanalytical chemistry are those for potential, current, and time. In this chapter several aspects relating to electrode potentials are considered current and time as well as further consideration of potentials are treated in Chapter 14. The electrode potentials involved in the classical galvanic cell are of considerable theoretical and practical significance for the understanding of many aspects not only of electroanalytical chemistry but also of thermodynamics and chemical equilibria, including the measurement of equilibrium constants. 

Electrochemistry provides a convenient and accurate way to measure equilibrium constants for many solution-phase reactions. For an overall cell reaction,... 

Measuring equilibrium constants is one of the most important applications of electrochemistry. Since A ° = 0 at equilibrium (no thermodynamic driving force for change) and Q = K, the Nernst equation can be rearranged to give 0.0592 V... 

Both involve high-pressure electrochemistry. One is the measurement of the pressure dependence of the rate constant for electron transfer in a given couple at an electrode, but it is not immediately clear how feg] and the corresponding volume of activation relate to feex and AV, respectively, for the self-exchange reaction of the same couple. This is a major theme of this chapter, and is pursued in detail below. The other method involves invocation of the cross relation of Marcus [5], which expresses the rate constant ku for the oxidation of, say, A by B+ in terms of its equilibrium constant and the rate constants kn and fe22 for the respective A+/A and B+/B self-exchange reactions ... 

Equilibrium electrochemistry, viz equilibrium electrochemical measurements, while being of fundamental importance since it allows thermodynamic parameters to be readily obtained (such as reaction free energies, entropies, equilibrium constants and solution pH), it is a rather dry subject and not as exciting as dynamic electrochemistry which is the main thrust of electrochemistry that is used commercially in numerous areas, such as in sensing and energy storage/generation. 

For a two-electrode cell, the net reaction comprises two half-reactions, involving the processes at the two electrodes. As already mentioned, usually only one of these processes is of interest, and this occurs at the working electrode in dynamic electrochemistry experiments or indicator electrode in equilibrium (potentiometric) experiments. The other electrode is made up such that it maintains a constant composition throughout the measurement, thus providing a reference potential. The most common reference for aqueous solution is the saturated calomel electrode (SCE), depicted in Fig. 1, and this provides... 

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