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Absolute electrode potential, in electrochemistry, according to an IUPAC definition,〔(IUPAC Gold Book - absolute electrode potential )〕 is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface). ==Definition== According to a more specific definition presented by Trasatti,〔Sergio Trasatti, "The Absolute Electrode Potential: an Explanatory Note (Recommendations 1986)", International Union of Pure and Applied Chemistry, Pure & AppL Chem., Vol. 58, No. 7, pp. 955–66, 1986. http://www.iupac.org/publications/pac/1986/pdf/5807x0955.pdf (pdf)〕 the absolute electrode potential is the difference in electronic energy between a point inside the metal (Fermi level) of an electrode and a point outside the electrolyte in which the electrode is submerged (an electron at rest in vacuum). This potential is difficult to determine accurately. For this reason, standard hydrogen electrode is typically used for reference potential. The absolute potential of the SHE is 4.44 ± 0.02 V at 25 °C. Therefore, for any electrode at 25 °C: : where: : is electrode potential :V is volt :''M'' denotes the electrode made of metal M :(abs) denotes the absolute potential :(SHE) denotes the electrode potential relative to the standard hydrogen electrode. A different definition for the absolute electrode potential (also known as absolute half-cell potential and single electrode potential) has also been discussed in the literature.〔Alan L. Rockwood, "Absolute half-cell thermodynamics: Electrode potential", Physical Review A, Vol 33, No. 1, pp. 554–59, 1986.〕 In this approach, one first defines an isothermal absolute single-electrode process (or absolute half-cell process.) For example, in the case of a generic metal being oxidized to form a solution-phase ion, the process would be :M(metal) → M+(solution) + (gas) For the hydrogen electrode, the absolute half-cell process would be :H2 (gas) → H+(solution) + (gas) Other types of absolute electrode reactions would be defined analogously. In this approach, all three species taking part in the reaction, including the electron, must be placed in thermodynamically well-defined states. All species, including the electron, are at the same temperature, and appropriate standard states for all species, including the electron, must be fully defined. The absolute electrode potential is then defined as the Gibbs free energy for the absolute electrode process. To express this in volts one divides the Gibb’s free energy by the negative of Faraday’s constant. Rockwood's approach to absolute-electrode thermodynamics is easily expendable to other thermodynamic functions. For example, the absolute half-cell entropy has been defined as the entropy of the absolute half-cell process defined above.〔Alan L. Rockwood, "Absolute half-cell entropy", Physical Review A, vol. 36, No. 3, pp. 1525–26, 1987.〕 An alternative definition of the absolute half-cell entropy has recently been published by Fang et al.〔Zheng Fang, Shaofen Wang, Zhenghua Zhang, and Guanzhou Qiu, "The electrochemical Peltier heat of the standard hydrogen electrode reaction", Thermochimica Acta, Vol. 473, pp. 40–44, 2008.〕 who define it as the entropy of the following reaction (using the hydrogen electrode as an example): :H2 (gas) → H+(solution) + (metal) This approach differs from the approach described by Rockwood in the treatment of the electron, i.e. whether it is placed in the gas phase or in the metal. 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「Absolute electrode potential」の詳細全文を読む スポンサード リンク
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