Electrochemical potential electromotive force

A special example of electrical work occurs when work is done on an electrochemical cell or by such a cell on the surroundings -w in the convention of this article). Themiodynamics applies to such a cell when it is at equilibrium with its surroundings, i.e. when the electrical potential (electromotive force emi) of the cell is... 

The overall electrochemical reaction is the electrolysis of water (Eqn (14.20)). The water electrolysis occurs if a voltage drop greater than its reversible potential (electromotive force) is applied to the ceU. The electromotive force can be calculated by the Nemst equation as follows ... 

Each metal or metal area will develop an electrode with a measurable electrical potential. This potential can be referenced to that of a standard hydrogen electrode, which by convention is set at zero. Thus, all metals have either a higher or lower potential compared to hydrogen, and a comparative list of metals can be produced indicating their relative nobility. This list is the galvanic or electrochemical series and measured as an electromotive force (EMF). 

Wagner pioneered the use of solid electrolytes for thermochemical studies of solids [62], Electrochemical methods for the determination of the Gibbs energy of solids utilize the measurement of the electromotive force set up across an electrolyte in a chemical potential gradient. The electrochemical potential of an electrochemical cell is given by ... 

Potentiometry deals with the electromotive force (EMF) generated in a galvanic cell where a spontaneous chemical reaction is taking place. In practice, potentiometry employs the EMF response of a galvanostatic cell that is based on the measurement of an electrochemical cell potential under zero-current conditions to determine the concentration of analytes in measuring samples. Because an electrode potential generated on the metal electrode surface,... 

An electrical potential difference between the electrodes of an electrochemical cell (called the cell potential) causes a flow of electrons in the circuit that connects those electrodes and therefore produces electrical work. If the cell operates under reversible conditions and at constant composition, the work produced reaches a maximum value and, at constant temperature and pressure, can be identified with the Gibbs energy change of the net chemical process that occurs at the electrodes [180,316]. This is only achieved when the cell potential is balanced by the potential of an external source, so that the net current is zero. The value of this potential is known as the zero-current cell potential or the electromotive force (emf) of the cell, and it is represented by E. The relationship between E and the reaction Gibbs energy is given by... 

To measure the electrode potential of a test electrodes, M, we usually use an electrochemical cell consisting of test electrode M and reference electrode both of which are coimected by a metal lead of A and A" of the same metallic conductor to a potentiometer outside the cell as shown in Fig. 4-23. The difference in the electrode potential, E, measured between the test electrode and the reference electrode, conventionally called the electromotive force, equals the difference in the Fermi level of electrons between the two electrodes E = - 8j(M) - EjtM )... 

Fig. 6-1. Electrochemical cell, electric charge flow in a closed cell circuit, and electron levels of two electrodes in an open cell circuit M = electrode S = electrolyte solution a, = real potential of electrons in electrode, e.Ji -electromotive force.

The electromotive force of an electrochemical cell is the difference in electrode potential between the two electrodes in the cell. According to the TUPAC convention, the electromotive force is the potential of the right hand electrode referred to the potential of the left hand electrode. We consider, for example, a hydrogen-oxygen cell shown in Fig. 6—4 the cell reaction is given by Eqn. 6-1 and the cell diagram is given by Eqn. 6-5 ... 

Fig. 6-4 Electromotive force Em, electron level a., and electrostatic potential profile for an electrochemical cell = inner potential.

The electrode potential of an electrode reaction at equilibrium can be measured as the electromotive force of an electrochemical cell composed of both the reaction electrode and the normed hydrogen electrode. The potential of the reaction electrode thus measured is taken as the equilibrium potential of the electrode reaction relative to the normal hydrogen electrode. 

Let us consider the general electrochemical cell shown in Figure 5.2. The potential difference across the electrochemical cell, denoted , is a measurable quantity called the electromotive force (EMF) of the cell. The potential difference in Figure 5.2 is made up of four contributions since there are four phase boundaries in this cell two metal-solution interphases and two metal-metal interfaces. The cell in Figure 5.2 can be represented schematically as Pt/M7S/M/Pt. 

L electromotive force, emf (in an electrochemical cell) equilibrium electrode potential in volts... 

As shown in Figure 18, the potential is almost proportional to the logarithm of H2 concentration diluted in air. When H2 is diluted in N2, the observed potential corresponds to the electromotive force of a H2-02 fuel cell, and in fact the EMF was as large as about 1.0 V with a theoretical slope of 30 mV/decade, as shown in the same figure. It has been shown that in the case of H2 diluted in air, the following electrode reaction, i.e., electrochemical oxidation of hydrogen (2) and electrochemical reduction of oxygen (3), are important. 

However, electrochemical cells are most conveniently considered as two individual half reactions, whereby each is written as a reduction in the form indicated by Equations2.ll and 2.12. When this is done and values of the appropriate quantities are inserted, a potential can be calculated for each half cell of the electrode system. Then the reaction corresponding to the half cell with the more positive potential will be the positive terminal in a galvanic cell, and the electromotive force of that cell will be represented by the algebraic difference between the potential of the more-positive half cell and the potential of the less-positive half cell ... 

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,... 

What is wrong with the following argument If the terminals of an electrochemical cell are constructed from the same metal, the chemical potential of electrons [species i in Eq. (36)] at the terminals, which depends only on T, P and concentrations, are the same. From Eq. (36), the electromotive force of the cell is therefore zero ... 

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