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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 RICE chart ： ウィキペディア英語版 RICE chart RICE chart, or RICE box is a tabular system of keeping track of changing concentrations in an equilibrium reaction. RICE stands for "''Reaction, Initial, Change, Equilibrium''".〔(General Chemistry Concepts - YouTube )〕 It is used in chemistry to keep track of the changes in amount of substance of the reactants and also organize a set of conditions that one wants to solve with. == Example == To illustrate the processes, consider the case of dissolving a weak acid, HA, in water. How can the pH be calculated? Note that in this example, we are assuming that the acid is not very weak, and that the concentration is not very dilute, so that the concentration of () ions can be neglected. This is equivalent to the assumption that the final pH will be below about 6 or so. See Calculations of pH for more details. First write down the equilibrium expression. This is generally regarded as the 'R'. :$HA\; \backslash rightleftharpoons\; A^-\; +\; H^+$ The columns of the table correspond to the three species in equilibrium. The first row, labeled I, has the initial conditions: the ''nominal concentration'' of acid is Ca and it is initially undissociated, so the concentrations of A− and H+ are zero. The second row, labeled C, specifies the change that occurs during the reaction. When the acid dissociates, its concentration changes by an amount ''-x'', and the concentrations of A− and H+ both change by an amount ''+x''. This follows from consideration of ''mass balance'' (the total number of each atom/molecule must remain the same) and ''charge balance'' (the sum of the electric charges before and after the reaction must be zero). Note that the coefficients in front of the "x" correlate to the mole ratios of the reactants to the product. For example, if the reaction equation had 2 H+ ions in the product, then the "change" for that cell would be "2x" The third row, labeled E, is the sum of the first two rows and shows the final concentrations of each species at equilibrium. It can be seen from the table that, at equilibrium, () = x. To find ''x'', the equilibrium constant must be specified. :$K\_a\; =\; \backslash frac$ Substitute the concentrations with the values found in the last row of the ICE table. $K\_a\; =\; \backslash frac$ $x^2\; +\; K\_a\; x\; -\; K\_a\; C\_a\; =\; 0$ With specific values for Ca and Ka this quadratic equation can be solved for x. Assuming〔Strictly speaking pH is equal to -log10 where is the activity of the hydrogen ion. In dilute solution concentration is almost equal to activity〕 that pH = -log10() the pH can be calculated as pH = -log10x. If the degree of dissociation is quite small, Ca ≫ x and the expression simplifies to :$K\_a\; =\; \backslash frac$ and pH= 1/2( p''K''a - log Ca). This approximate expression is good for p''K''a values larger than about 2 and concentrations high enough. 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「RICE chart」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.