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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 Eley-Rideal mechanism ： ウィキペディア英語版 Reactions on surfaces Reactions on surfaces are reactions in which at least one of the steps of the reaction mechanism is the adsorption of one or more reactants. The mechanisms for these reactions, and the rate equations are of extreme importance for heterogeneous catalysis. Via scanning tunneling microscopy, it is possible to observe reactions at the solid|gas interface in real space, if the time scale of the reaction is in the correct range. Reactions at the solid|gas interface are in some cases related to catalysis. ==Simple decomposition== If a reaction occurs through these steps: : A + S (unicode:⇌) AS → Products where A is the reactant and S is an adsorption site on the surface and the respective rate constants for the adsorption, desorption and reaction are ''k''1, ''k''−1 and ''k''2, then the global reaction rate is: :$r=-\backslash frac\; =k\_2\; C\_=k\_2\; \backslash theta\; C\_S$ where: * ''r'' is the rate, ''m''−2s−1 *$C\_$ is the surface concentration of occupied sites, ''m''−2 *$\backslash theta$ is the surface coverage, dimensionless *$C\_S$ is the total number of sites (occupied or not), ''m''−2 * ''t'' is time, ''s'' * ''k''2 is the kinetic constant for the surface reaction, ''s''−1. $C\_S$ is highly related to the total surface area of the adsorbent: the greater the surface area, the more sites and the faster the reaction. This is the reason why heterogeneous catalysts are usually chosen to have great surface areas (in the order of a hundred ''m''2/gram) If we apply the steady state approximation to AS, then: : $\backslash frac\; =\; 0\; =\; k\_1\; C\_A\; C\_S\; (1-\backslash theta)-\; k\_2\; \backslash theta\; C\_S\; -k\_\backslash theta\; C\_S$ so $\backslash theta\; =\backslash frac$ and : $r=-\backslash frac\; =\; \backslash frac\; .$ Note that, with $K\_1=\backslash frac$. The result is completely equivalent to the Michaelis–Menten kinetics. The rate equation is complex, and the reaction order is not clear. In experimental work, usually two extreme cases are looked for in order to prove the mechanism. In them, the rate-determining step can be: *Limiting step: adsorption/desorption :$k\_2\; \backslash gg\; \backslash \; k\_1C\_A,\; k\_,\backslash textr\; \backslash approx\; k\_1\; C\_A\; C\_S.$ The order respect to A is 1. Examples of this mechanism are N2O on gold and HI on platinum *Limiting step: reaction :$k\_2\; \backslash ll\; \backslash \; k\_1C\_A,\; k\_\backslash text\backslash theta\; =\backslash frac$. Depending on the concentration of the reactant the rate changes: : * Low concentrations, then $r=\; K\_1\; k\_2\; C\_A\; C\_S$, that is to say a first order reaction in component A. : * High concentration, then $r=\; k\_2\; C\_S$. It is a zeroth order reaction in component A. 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「Reactions on surfaces」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.