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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Self-ionization of water ： ウィキペディア英語版 Self-ionization of water The self-ionization of water (also autoionization of water, and autodissociation of water) is an ionization reaction in pure water or an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−. The hydrogen nucleus, H+, immediately protonates another water molecule to form hydronium, H3O+. It is an example of autoprotolysis, and exemplifies the amphoteric nature of water. ==Equilibrium constant== Chemically pure water has an electrical conductivity of 0.055 µS∙cm−1. According to the theories of Svante Arrhenius, this must be due to the presence of ions. The ions are produced by the self-ionization reaction :H2O + H2O H3O+ + OH− This equilibrium applies to pure water and any aqueous solution. Expressed with activities , instead of concentrations, the thermodynamic equilibrium constant for the water ionization reaction is: :$K\_\; =\; \backslash frac\}\}$ which is numerically equal to the more traditional thermodynamic equilibrium constant written as: :$K\_\; =\; \backslash frac\}\}$ under the assumption that the sum of the chemical potentials of H+ and H3O+ is formally equal to twice the chemical potential of H2O at the same temperature and pressure.〔("Release on the Ionization Constant of H2O" ) The International Association for the Properties of Water and Steam, Lucerne, Switzerland, August 2007.〕 Because the activity of water, as the solvent in a very dilute solution, is assumed to be unity, the ionic product of water can be also expressed on an activity basis as:〔IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006–) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook. (Entry: autoprotolysis constant ).〕 :$K\_=a\_\}$ In dilute aqueous solutions, the activities of the solute particles are essentially equal to their concentrations. Thus, the ionization constant, dissociation constant, self-ionization constant, or ionic product of water, symbolized by ''K''w, may be given by: :$K\_=()()$ where () is the concentration of hydrogen or hydronium ion, and () is the concentration of hydroxide ion. At 25 °C ''K''w is equal to (mol/L)2. Note that the units are concentration squared. We can also define $\backslash mathrmK\_\; =\; -\backslash log\_\; K\_\; =\; 14$ at 25 °C. This is analogous to the notations pH and p''K''a for an acid dissociation constant, where the symbol p denotes a cologarithm. The logarithmic form of the equilibrium constant equation is $\backslash mathrmK\_\; =\; \backslash mathrm\; +\; \backslash mathrm$. 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「Self-ionization of water」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.