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A concentration cell is a limited form of a galvanic cell that has two equivalent half-cells of the same material differing only in concentrations. One can calculate the potential developed by such a cell using the Nernst Equation. A concentration cell produces a small voltage as it attempts to reach equilibrium. This equilibrium occurs when the concentration of reactant in both cells are equal. Because an order of magnitude concentration difference produces less than 60 millivolts at room temperature, concentration cells are not typically used for energy storage. Concentration cells generate electricity from the thermodynamic free energy that can be extracted from the difference in chemical concentrations of reactants, in the same reaction. This energy is generated from thermal energy that the cells absorb as heat, as the electricity flows. This generation of electricity from ambient thermal energy, without a temperature gradient, is possible because the convergence of chemical concentrations in the two cells increases entropy, and this increase more than compensates for the entropy decreased when heat is converted into electrical energy. Concentration cell methods of chemical analysis compare a solution of known concentration with an unknown, determining the concentration of the unknown via the Nernst Equation or comparison tables against a group of standards. Concentration cell corrosion occurs when two or more areas of a metal surface are in contact with different concentrations of the same solution. There are three general types of concentration cells. ==Metal ion concentration cells== In the presence of water, a high concentration of metal ions will exist under faying surfaces and a low concentration of metal ions will exist adjacent to the crevice created by the faying surfaces. An electrical potential will exist between the two points. The area of the metal in contact with the high concentration of metal ions will be cathodic and will be protected, and the area of metal in contact with the low metal ion concentration will be anodic and corroded. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Concentration cell」の詳細全文を読む スポンサード リンク
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