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Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is the mole. It has the unit symbol mol. The mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 12 g of the isotope carbon-12. This number is called Avogadro's number and has the value It is the numerical value of the Avogadro constant which has the unit 1/mol, and relates the molar mass of an amount of substance to its mass. Therefore, the amount of substance of a sample is calculated as the sample mass divided by the molar mass of the substance. Amount of substance appears in thermodynamic relations such as the ideal gas law, and in stoichiometric relations between reacting molecules as in the law of multiple proportions. The only other unit of amount of substance in current use is the pound-mole with the symbol lb-mol, which is sometimes used in chemical engineering in the United States. One pound-mole is .〔This relation is exact, from the definition of the international avoirdupois pound.〕 ==Terminology== When quoting an amount of substance, it is necessary to specify the entity involved, unless there is no risk of ambiguity. One mole of chlorine could refer either to chlorine atoms, as in 58.44 g of sodium chloride, or to chlorine molecules, as in 22.711 liters of chlorine gas at STP. The simplest way to avoid ambiguity is to replace the term ''substance'' by the name of the entity or to quote the empirical formula. For example: * amount of chloroform (molecules), CHCl3 * amount of sodium (atoms), Na * amount of hydrogen (atoms), H * ''n''(C2H4) This can be considered to be a technical definition of the word ''amount'', a usage which is also found in the names of certain derived quantities (see below). 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「amount of substance」の詳細全文を読む スポンサード リンク
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