Voltaic cells defined

The Volta potential is defined as the difference between the electrostatic outer potentials of two condensed phases in equilibrium. The measurement of this and related quantities is performed using a system of voltaic cells. This technique, which in some applications is called the surface potential method, is one of the oldest but still frequently used experimental methods for studying phenomena at electrified solid and hquid surfaces and interfaces. The difficulty with the method, which in fact is common to most electrochemical methods, is lack of molecular specificity. However, combined with modem surface-sensitive methods such as spectroscopy, it can provide important physicochemical information. Even without such complementary molecular information, the voltaic cell method is still the source of much basic electrochemical data. 

The surface potential of a liquid solvent s, %, is defined as the difference in electrical potentials across the interface between this solvent and the gas phase, with the assumption that the outer potential of the solvent is zero. The potential arises from a preferred orientation of the solvent dipoles in the free surface zone. At the surface of the solution, the electric field responsible for the surface potential may arise from a preferred orientation of the solvent and solute dipoles, and from the ionic double layer. The potential as the difference in electrical potential across the interface between the phase and gas, is not measurable. However, the relative changes caused by the change in the solution s composition can be determined using the proper voltaic cells (see Sections XII-XV). 

Thus the Volta potential may be operationally defined as the compensating voltage of the cell. Very often the terms Volta potential and compensation voltage are used interchangeably. It should be stressed that the compensating voltage of a voltaic cell is not always the direct measure of the Volta potential. 

The cathode is defined as the electrode at which reduction occurs, i.e., where electrons are consumed, regardless of whether the electrochemical cell is an electrolytic or voltaic cell. In both electrolytic and voltaic cells, the electrons flow through the wire from the anode, where electrons are produced, to the cathode, where electrons are consumed. In an electrolytic cell, the dc source forces the electrons to travel nonspontaneously through the wire. Thus, the electrons flow from the positive electrode (the anode) to the negative electrode (the cathode). However, in a voltaic cell, the electrons flow spontaneously, away from the negative electrode (the anode) and toward the positive electrode (the cathode). 

There is another way in which electrons can be rearranged in a chemical reaction, and that is through a wire. Electrochemistry is redox chemistry wherein the site for oxidation is separated from the site for reduction. Electrochemical setups basically come in two flavors electrolytic and voltaic (also known as galvanic) cells. Voltaic cells are cells that produce electricity, so a battery would be classed as a voltaic cell. The principles that drive voltaic cells are the same that drive all other chemical reactions, except the electrons are exchanged though a wire rather than direct contact. The reactions are redox reactions (which is why they produce an electron current) the reactions obey the laws of thermodynamics and move toward equilibrium (which is why batteries run down) and the reactions have defined rates (which is why some batteries have to be warmed to room temperature before they produce optimum output). 

Redox potential is defined by the half cell reduction potential that is created by redox couples that are primarily due to GSH, NAD+ and nicotinamide dinucleotide phosphate. These couples are in ratios of the oxidized to reduced form of the molecules (NAD /NAD, NADP /NADPH, and GSSG/2GSH). The redox couples can be independent, as well linked to each other to form related couples. The redox environment is a reflection of these couples. These ratios can be measured by the Nemst equation, similar to a voltaic cell. 

Now we can construct a voltaic cell consisting of this reference half-cell and another half-cell whose potential we want to determine. With E eference defined as zero, the overall Eceii allows us to find the unknown standard electrode potential. 

An electrochemical cell can be defined as two conductors or electrodes, usually metallic, immersed in the same electrolyte solution, or in two different electrolyte solutions which are in electrical contact. Electrochemical cells are classed into two groups. A galvanic (sometimes, voltaic) cell is one in which electrochemical reactions occur spontaneously when the two electrodes are connected by a conductor. These cells are often employed to convert chemical energy into electrical energy. Many types are of commercial Importance, such as the lead-acid battery, flashlight batteries, and various fuel cells. An electrolytic cell is one in which chemical reactions are... 

The Volta potential, A ip(MX), can also be considered in the case of immiscible electrolyte solutions, e.g. for the nonpolarizable water-nitrobenzene interface in the state of distribution equihbrium of the MX electrolyte (Fig. 1). The above potential can be operationally defined as the compensating voltage of the voltaic cell [163] ... 

Conditions (1) and (4) are typical for all investigations of the Volta potentials. There are no serious problems with reahzing condition (2). It is also important to satisfy this condition in the studies of the differences of distribution potentials with the use of Eq. (35), i.e. by the method of voltaic cells [68-78]. In the above investigations, type-XVII cells are employed. As it can be easily proved, substitution of the electrolyte M X by M2X2, when the conditions (1), (2), and (4) are satisfied, leads to a change of the compensation voltage, AE17, defined by the equation ... 

In 1800 Volta described the first voltaic pile or galvanic cell , i.e. a source of direct electric current at low potential. The first cell was made from discs of copper and zinc separated from each other by a cloth saturated with salt solution. Ever since then, the search for better cells to supply electricity has continued. This section will start by classifying the various kinds of batteries and fuel cells, proceed to describe some of the principles of operation and define the efficiency of the cells, and then describe the general features of each kind of cell. 

Operation of a singular cell is often defined by the current-voltage curve, as with voltaic batteries. Seeing as there are many differences between fuel cells and... 

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