Electromotive force of an electrochemical cell

The voltage of an electrochemical cell is a thermodynamic order of magnitude it is the difference in potential which is established, with a current of strictly zero, between the two electrodes. The absolute value (i.e. regardless of the sign) is called the electromotive force of the cell (eml) and 

56 The Normal Hydrogen Electrode (NHE) corresponds to the following redox reaction  

It corresponds to the cell Pt/H2 (gaseous)/H30 with a concentration of hydronium ions H3O equal to 1 mol/L. 

In standard conditions, the electromotive force measured is called the standard electromotive force standard and notated at AE°. 

We have just defined the electromotive force of an electrochemical cell for standard conditions. Yet these conditions are not very realistic, or at least are very limited in terms of a chemical reaction during which the concentrations of the reagents are different from standard conditions or change. 

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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 ... 

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. 

The Gibbs energy change is related to some other important physical quantities, such as the equilibrium constant for a chemical reaction and the electromotive force of an electrochemical cell, by the Nemst and van t Hoff equations ... 

The Nemst equation applies (if we neglect the activity coefficients of the ions, in keeping with PB theory) to the emf (electromotive force) of an electrochemical cell. The emf of such a cell and the surface potential of a colloidal particle are quantities of quite different kinds. It is not possible to measure colloidal particle with a potentiometer (where would we place the electrodes ), and even if we could, we have no reason to expect that it would obey the Nemst equation. We have been at pains to point out that all the experimental evidence on the n-butylam-monium vermiculite system is consistent with the surface potential being roughly constant over two decades of salt concentration. This is clearly incompatible with the Nemst equation, and so are results on the smectite clays [28], Furthermore, if the zeta potential can be related to the electrical potential difference deviations from Nemst behavior, as discussed by Hunter... 

This principle is used every time one measures the electromotive force of an electrochemical cell. In this case the potential measuring device determines the difference between the electrochemical potentials of electrons in two pieces of the same metal, for example, in two copper wires. The classical device for doing this measurement is a Poggendorf compensation potentiometer but a modern in-... 

This process is based on the relationship between the concentration of the ion located in the solution and the electromotive force of an electrochemical cell in which this ion is one of the components. 

Cell potential (13.2) The electromotive force of an electrochemical cell. The amount of work the cell can do per coulomb of charge. 

E standard electric potential or standard electromotive force of an electrochemical cell... 

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... 

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 ... 

In general, the electromotive force E of an electrochemical cell is given by Eq. 9.27 ... 

Wagner equation — denotes usually one of two equations derived by -> Wagner for the flux of charged species Bz under an -> electrochemical potential gradient, and for the - electromotive force of a -> galvanic cell with a mixed ionic-electronic -> conductor [i-v] ... 

C. The potentiometric determination of pH The most advanced and precise method of the measurement of pH is based on the measurement of the electromotive force (e.m.f.) of an electrochemical cell, which contains the solution of the unknown pH as electrolyte, and two electrodes. The electrodes are connected to the terminals of an electronic voltmeter, most often called simply a pH-meter. If properly calibrated with a suitable buffer of a known pH, the pH of the unknown solution can be read directly from the scale. 

This allows us to predict the electromotive force (EMF), , of an electrochemical cell under a specified set of conditions. The EMF under standard conditions is easily predicted from tables of data and gives us the standard EMF usually denoted by The relationship between these quantities... 

The Nernst equation gives the electromotive force (EMF) G of an electrochemical cell as a function of the absolute temperature T as... 

The potential of an electrochemical cell, also known as the cell potential or electromotive force (emf) is the sum of the potential drops at the cathode and anode, where the reduction and oxidation reactions occur. With the introduction of a reference electrode the potentials of these two electrodes can be measured independently, allowing the independent investigation of the reactions that are taking place at each electrode (working or counter). These redox reactions are called half-cell reactions or simply half-reactions. The halfreaction potential can be measured with a SHE electrode at standard conditions, i.e., at electrolyte concentrations of 1 M, gas pressures of 1 atm., and... 

Electrochemical gas sensors detect gases based on the electromotive force(EMF) or the current of an electrochemical cell due to the electrochemical reaction of a particular gas. Solid electrolyte which a specific ion can selectively permeate is used as a diaphragm. Potentiometric type gas sensors have been most widely adopted. Among them potentiometric oxygen sensors composed of partial stabilized zirconia have already had practical application and heen extensively used for the feedback control of the air-fuel ratio of automobile engines. The oxygen sensor elements are composed of the following electrochemical cell. 

Applications of potentiometry involve the use of an electrochemical cell consisting of a reference electrode of constant potential and an indicator electrode that responds to the analyte studied and sample composition. The electromotive force (e.m.f.) of this cell can be regarded as the difference of the potentials of the two electrodes (half-cells). 

Counter Electromotive Force A voltage of an electrochemical cell opposite to the applied external voltage. Also referred to as back EMF. 

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