|
In chemistry, the mole fraction or molar fraction () is defined as the amount of a constituent (expressed in moles), , divided by the total amount of all constituents in a mixture, : : The same concept expressed with a denominator of 100 is the mole percent or molar percentage or molar proportion (mol%). The mole fraction is also called the amount fraction.〔 It is identical to the number fraction, which is defined as the number of molecules of a constituent divided by the total number of all molecules . The mole fraction is sometimes denoted by the lowercase Greek letter '''' (''chi'') instead of a Roman . For mixtures of gases, IUPAC recommends the letter .〔 The National Institute of Standards and Technology of the United States prefers the term amount-of-substance fraction over mole fraction because it does not contain the name of the unit mole. Whereas mole fraction is a ratio of moles to moles, molar concentration is a ratio of moles to volume. The mole fraction is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction (percentage by weight, wt%) and volume fraction (percentage by volume, vol%) are others. ==Properties== Mole fraction is used very frequently in the construction of phase diagrams. It has a number of advantages: * it is not temperature dependent (such as molar concentration) and does not require knowledge of the densities of the phase(s) involved * a mixture of known mole fraction can be prepared by weighing off the appropriate masses of the constituents * the measure is ''symmetric'': in the mole fractions x=0.1 and x=0.9, the roles of 'solvent' and 'solute' are reversed. * In a mixture of ideal gases, the mole fraction can be expressed as the ratio of partial pressure to total pressure of the mixture 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「mole fraction」の詳細全文を読む スポンサード リンク
|