Electromotive potential difference

The electromotive potential difference ( jj) measured in volts may be related to the corresponding contribution to the Gibbs free energy (4>i — 2) by... 

When strips of reactive metals such as zinc are placed in water a potential difference, die electromotive force (emf), is set up die metal becomes negatively charged due to die transfer of zinc ions to die solution and die build-up of electrons on die metal. The metal strips or rods are termed die... 

Electric pofcTidfff, ), potential difference, or electromotive force (emf, E, e) have units of volts and refer to the energy change when a charge is moved from one point to another m an electric field. 

The theory of Kelvin (1854), developed in the preceding, section, stands midway between these two hypotheses, in that it assumes the existence of potential differences at the junctions, playing the role postulated by Clausius, and also admits the production of electromotive forces in the interior of the homo-, geneous wires due to inequalities of temperature in the latter, these inequalities giving rise to the flow of heat which is regarded as essential in the theory of Kohlrausch. 

Table 6.11 lists, to the right of the arrows, reducing agents or disposition to electron loss or disposition to oxidation in order of increasing strength. Such a list is more popularly called the electromotive force, or emf, series. The maximum potential difference which can be measured for a given cell is called the electromotive force (abbreviated emf) and represented by the symbol Ecell. It may be recounted that the emf values reported in Table 6.11 are for those cells under specified standard conditions in which all the concentrations are 1 M and pressures are 1 atm. The emf of such a cell is said to be its standard electromotive force, and is given by the symbol E ell. 

It is relevant to follow up the description given above on reversible electrodes with attention focused on the potential difference of a cell. The potential difference measured under reversible conditions, is called the electromotive force, or emf, of the cell, E. It is clear that if a cell is reversible then it is implied that the half-cells of which it is composed are also reversible. 

As has already been mentioned, the EMF the electromotive force) of a cell is given by the potential difference between leads of identical metallic material. In view of this, a galvanic cell is represented schematically as having identical metallic phases at either end. 

While the voltage of the cell represents the potential difference between the two terminals of the battery, in reality it relates to the separation in energy between the two half-cells. We call this separation the emf where the initials derive from the archaic phrase electromotive force. An emf is defined as always being positive. 

The term emf follows from the archaic term electromotive force . Physicists prefer to call the emf a potential difference or symbolize it as a p.d. . 

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... 

The acronym emf derives from the somewhat archaic term electromotive force . Physicists tend to employ the term potential difference (and abbreviate it to pd ). Another term that is used is fceii (cell potential). 

The portion AQ = AH - AG = TAS of AH is transformed into heat. Ideal theoretical efficiencies % determined by the types and amounts of reactants and by the operating temperature. Fuel cells have an efficiency advantage over combustion engines because the latter are subdued to the Carnot limitation. High thermodynamic efficiencies are possible for typical fuel cell reactions (e.g., e,h = 0.83 (at 25°C) for H2 + I/2O2 -> H20(i)). The electrical potential difference between anode and cathode, = -AG/W(f, which is also called the electromotive force or open-circuit voltage, drives electrons through the external... 

In a redox reaction, the energy released in a reaction due to movement of charged particles gives rise to a potential difference. The maximum potential difference is called the electromotive force (FMF), E, and the maximum electric work, W, is the product of charge q in Coulombs (C), and the potential NE in volts or FMF ... 

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. 

A quantity (commonly symbolized by V) for the work needed to bring a unit positive charge to that point in space from an infinite distance. Thus, V = dw/dQ where w is the work and Q is the electric charge. The SI unit for electric potential is the volt (V). The electric potential difference, also measured in volts and symbohzed by U, Ay, or Acb, is equal to the difference in potential between two points U = V2 as measured by the work needed to transfer a unit positive charge from one point to the other. See also Electromotive Force... 

Electromagnetic A change in the intensity or direction of a magnetic field resulting in an electromotive force in any conductor within the field V = -dcb/df where V is the induced potential difference, cb is the magnetic flux, and t is time. 3. Electrostatic The process by which an electron charge is produced on a conductor due to the influence of an electric field. 

In a similar though less diabolical manner, the electrons produced at the anode of a voltaic cell have a natural tendency to flow along the circuit to a location with lower potential the cathode. This potential difference between the two electrodes causes the electromotive force, or EMF, of the cell. EMF is also often referred to as the cell potential and is denoted fj.g,. The cell potential varies with temperature and concentration of products and reactants and is measured in volts (V). The standard cell potential, or E° gn, is the that occurs when concentrations of solutions ire all at 1 M and the cell is at standard temperature and pressure (STP). 

Electric potential, potential difference, electromotive force volt V W/A m2 kg/(s3 A)... 

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,... 

This process leads to the development of a voltage difference between anode and cathode and when the external circuit is open , this potential difference is the electromotive force (the e.m.f.) of the cell. When there is an electrical load in the external circuit, for example a motor, then a current will flow and electrochemical energy is converted into mechanical energy. 

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