Forces, EMF

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... 

ASTM E230-96el. Standard Specification for Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples. American Society for Testing and Materials, 1996. 

As a result, the electromotive force (EMF) of the cell is zero In the presence of fluoride ions, cerium(IV) forms a complex with fluoride ions that lowers the cerium(IV)-cerium(IIl) redox potential The inner half-cell is smaller, and so only 5 mL of cerium(IV)-cenum (III) solution is added To the external half-cell, 50 mL of the solution is added, but the EMF of the cell is still zero When 10 mL of the unknown fluonde solution is added to the inner half-cell, 100 mL of distilled water IS added to the external half-cell The solution in the external half-cell is mixed thoroughly by turning on the stirrer, and 0 5 M sodium fluonde solution is added from the microburet until the null point is reached The quantity of known fluonde m the titrant will be 10 times the quantity of the unknown fluoride sample, and so the microburet readings must be corrected prior to actual calculations... 

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. 

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). 

Cathodic protection apparatuses are well proven, widely used devices and are not to be confused with magnetic devices gadgets ) or other similar but generally less than satisfactory items of capital equipment. Cathodic protection devices reverse the tendency of a metal to go into solution at the anode (corrosion) by the application of a counter-potential. This counter-potential or electromotive force (EMF) is provided either from a permanent external source such as a battery or rectifier or from the installation of a sacrificial anode. 

This gives a standard electromotive force (EMF) at equilibrium... 

E electromotive force (EMF), electrode potential, electric field strength,... 

The concentration overpotential i/c is the component of the overpotential due to concentration gradients in the electrolyte solution near the electrode, not including the electric double layer. The concentration overpotential is usually identified with the Nernst potential of the working electrode with respect to the reference electrode that is, the thermodynamic electromotive force (emf) of a concentration cell formed between the working electrode (immersed in electrolyte depleted of reacting species) and the reference electrode (of the same kind but immersed in bulk electrolyte solution) ... 

The electromotive force (emf) across the cell is a sum of several potentials many of them are sample independent ... 

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... 

All three of these terms have units of ohms as they are all measures of some form of resistance to electrical flow. The reactance of an inductor is high and comes specifically from the back electromotive force (EMF p. 46) that is generated within the coil. It is, therefore, difficult for AC to pass. The reactance of a capacitor is relatively low but its resistance can be high therefore, direct current (DC) does not pass easily. Reactance does not usually exist by itself as each component in a circuit will generate some resistance to electrical flow. The choice of terms to define total resistance in a circuit is, therefore, resistance or impedance. 

To recall the basic concepts of the thermodynamics of cell operation, such as the electrode potential E, the standard electrode potential and the electromotive force (emf). 

The electromotive force (emf) of liquid membrane electrodes depends on the activity of the ions in solution and their performance is similar in principle to that of the glass electrode. To characterize the behavior of liquid membrane electrodes, the linearity of the emf measurements vs. concentration of a certain ion in solution is checked. Additional performance data are the Nernstian slope of the linear range and the pH range over which the potential of the electrode is constant. 

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. 

Electronically active chips (e.g.. Nanogen s NanoChip Electronic Microarray) are true microchips in which microelectrodes (pads) become elements of the array (Figure 2.13). The microelectrodes are covered with materials that allow immobilization of probes. Each electrode is individually addressable so that specific probes can be attached to different electrodes. Hybridization is accelerated by electromotive force (emf) on the target. Enhanced stringency is also achieved by modulation of the emf (Heller et al., 2000). 

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