Electrochemistry cell potential, electrical work

An electrochemical cell generates a potential difference E. (The symbol E, commonly used in electrochemistry, refers to electromotive force, an archaic term for potential difference.) The electrical work done when n moles of electrons is passed by the cell can be found using Eq. (15-1), w = -nFE. It can be shown that the electrical work done by an electrochemical cell, at constant temperature and pressure, is equal to the change in Gibbs free energy of the cell components,... 

Recall from Chapter 16 that an object s potential energy is due to its position or composition. In electrochemistry, electrical potential energy is a measure of the amount of current that can be generated from a voltaic cell to do work. Electric charge can flow between two points only when a difference in electrical potential energy exists between the two points. In an electrochemical cell, these two points are the two electrodes. The potential difference of a voltaic cell is an indication of the energy that is available to move electrons from the anode to the cathode. 

At the heart of electrochemistry is the electrochemical cell. We will consider the creation of an electrochemical cell from the joining of two half-cells. When an electrical conductor such as a metal strip is immersed in a suitable ionic solution, such as a solution of its own ions, a potential difference (voltage) is created between the conductor and the solution. This system constitutes a half-cell or electrode (Fig. 15.1). The metal strip in the solution is called an electrode and the ionic solution is called an electrolyte. We use the term electrode to mean both the solid electrical conductor in a half-cell (e.g., the metal strip) and the complete half-cell in many cases, for example, the standard hydrogen electrode, the calomel electrode. Each half-cell has its own characteristic potential difference or electrode potential. The electrode potential measures the ability of the half-cell to do work, or the driving force for the half-cell reaction. The reaction between the metal strip and the ionic solution can be represented as... 

Sep. 5,1870, Colombo, Ceylon (British Empire), now Sri Lanka - Dec. 16,1956, Canterbury, Kent, UK). Donnan was a British chemist who greatly contributed to the development of colloid chemistry, physical chemistry, and electrochemistry [i—iii]. In different periods of his life, he was working with van t - Hoff, -> Ostwald, F. W., and Ramsay. In electrochemistry, he studied (1911) the electrical potential set-up at a semipermeable membrane between two electrolytes [iv], an effect of great importance in living cells [v], Donnan is mostly remembered for his theory of membrane equilibrium, known as - Donnan equilibrium. This equilibrium results in the formation of - Donnan potential across a membrane. 

Electrochemistry works using the principles of oxidation-reduction reactions which generate electric currents or, more simply, the conversion of chemical information into an electrical signal. Electrochemical cells or sensors usually contain a working electrode, to which a potential is applied, and a reference electrode. The oxidation-reduction reaction that ensues is then recorded as an electric current which is a measurement of the analyte from the reaction. Electrochemical methods can be further subdivided into amperometric (measures current), potentiometric (measures potential), conductometric (measures the conductive properties of the medium), impedimetric (measures resistance and reactance) or field effect (measures current through charge accumulation at a gate electrode). ... 

Many experiments with voltaic cells ( piles ) were made by M. Berthelot. He tried to compare affinity and electromotive force by finding the e.m.f. of a cell which caused electrolysis with evolution of bubbles of gas, and attempted to connect this with the heat of reaction. He later recognised the significance of entropy changes, and experimented with liquid cells and liquid contact potentials, oxidation and reduction, acid-base neutralisation, etc., also the effect of superposition of an alternating current. Berthelot was not really at home in electrochemistry and his work is hardly ever mentioned. Experiments with several types of cells made by Hittorf gave appreciable differences between the chemical and electrical energies. 

The claims that he underestimated the historical achievements of Russian scientists did hurt Frumkin, however, and briefly he turned his attention to the history of electrochemistry in Russia in order to reevaluate Russian contributions. He rated the studies of Moritz Hermann von Jacobi (21 September 1801-10 March 1874) most highly. (The Russian version of his name is Boris Semyonovich Yakobi. ) Jacobi had discovered the maximum power theorem, and his name is also associated with the development of galvanic cells for testing electric motors. In addition, Frumkin noted the priority of Pyotr Romanovich Bagration (24 September 1818-17 January 1876), who had created the first galvanic dry cell in 1843. Finally, Frumkin drew attention to the work of Kazan professor Robert Andreyevich Colley (Kolli) (25 June 1845-2 August 1891) back in 1878. Colley was the first person to use the shift of the electrode potential in a certain period of time as a measure of the interfacial capacitance and found a value of 150 pF cm for platinum. 

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