Equivalent - Toryo

A fixed amount assigned to each element or compound based on the quantitative relationships of substances in a chemical reaction; also known as a chemical equivalent. In addition, when there is additivity in the physicochemical properties of a compound, the fixed amount of that property assigned to each atom and bonding pattern can also be called an equivalent (e.g., refraction equivalent). [ I ] Elemental equivalent: A number that represents the weight of the element that combines with oxygen (8,000). Since the atomic valence of oxygen is 2, the equivalent is equal to the atomic weight of that element divided by the atomic valence. J. Dalton initially took hydrogen, which has the smallest equivalent, and set this as 1 as the standard for equivalent, but later, J. J. Berzelius and others used 8,000, half the atomic weight of oxygen, as the standard. Currently, atomic weights are based on ^12C = 12.000, so the atomic weight of oxygen is 15.9994, and therefore the equivalent is 7.9997, but in reality it is equal to 8.000. [ II ] Acid and base equivalent: The amount of acid containing one equivalent of hydrogen that acts as an acid, and the amount of base sufficient to neutralize it. [ III ] Oxidizing and reducing agent equivalent: The amount of reducing agent containing one equivalent of hydrogen that participates in the reducing action, and the equivalent amount of oxidizing agent. The term equivalent has been abolished by the SI Committee along with regulations (degrees), and it is recommended that all amounts be expressed in terms of the amount of substance.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

化学反応における物質の量的関係にもとづいて，各元素または化合物ごとにわりあてられた一定量で，化学当量ともいう．また，化合物の物理化学的性質に加成性がある場合に，各原子および結合様式に対してわりあてられたその性質の一定量を当量ということもある(例：屈折当量)．【Ⅰ】元素の当量：酸素8.000の重量に対して，これと化合する元素の重量を表す数．酸素の原子価は2であるから，当量はその元素の原子量を原子価で割ったものに等しい．当量の基準として，最初，J. Dalton(ドルトン)は，もっとも当量の小さい水素をとり，これを1としたが，その後，J.J. Berzelius(ベルセリウス)らは，酸素の原子量の1/2の8.000を基準とした．現在，原子量は ¹²C ＝ 12.000を基準にしているから，酸素の原子量は15.9994，したがって当量は7.9997となるが，実際上8.000に等しい．【Ⅱ】酸および塩基の当量：酸として作用する水素の1当量を含む酸の量，およびこれを中和するだけの塩基の量．【Ⅲ】酸化剤および還元剤の当量：還元作用にあずかる水素の1当量を含む還元剤の量，およびこれに相当する酸化剤の量．当量という用語はSI委員会によって規定(度)とともに廃止し，すべて物質量で表現するように勧告されている．

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