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The Avogadro constant, commonly denoted N A [1] or L, [2] is an SI defining constant with an exact value of 6.022 140 76 × 10 23 mol −1 (reciprocal moles). [3] [4] It is this defined number of constituent particles (usually molecules, atoms, ions, or ion pairs—in general, entities) per mole and used as a normalization factor in relating the amount of substance, n(X), in a sample of a ...
These include the Boltzmann constant, which gives the correspondence of the dimension temperature to the dimension of energy per degree of freedom, and the Avogadro constant, which gives the correspondence of the dimension of amount of substance with the dimension of count of entities (the latter formally regarded in the SI as being dimensionless).
which is a constant for a fixed pressure and a fixed temperature. An equivalent formulation of the ideal gas law can be written using Boltzmann constant k B, as =, where N is the number of particles in the gas, and the ratio of R over k B is equal to the Avogadro constant. In this form, for V/N is a constant, we have
Avogadro, who inspired the Avogadro constant. The history of the mole is intertwined with that of units of molecular mass, and the Avogadro constant. The first table of standard atomic weight was published by John Dalton (1766–1844) in 1805, based on a system in which the relative atomic mass of hydrogen was defined as 1.
The Boltzmann constant and the Avogadro constant were similarly determined, which separately relate energy to temperature and particle count to amount of substance. The gas constant R is defined as the Avogadro constant N A multiplied by the Boltzmann constant k (or k B ):
For his work with gases a century prior, the physical constant that bears his name (the Avogadro constant) is the number of atoms per mole of elemental carbon-12 (6.022 × 10 23 mol −1). This specific number of gas particles, at standard temperature and pressure (ideal gas law) occupies 22.40 liters, which is referred to as the molar volume .
Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerreto [1] (/ ˌ æ v ə ˈ ɡ ɑː d r oʊ /, [2] also US: / ˌ ɑː v-/, [3] [4] [5] Italian: [ameˈdɛːo avoˈɡaːdro]; 9 August 1776 – 9 July 1856) was an Italian scientist, most noted for his contribution to molecular theory now known as Avogadro's law, which states that equal volumes of gases under the same conditions of ...
In chemistry, the amount of substance (symbol n) in a given sample of matter is defined as a ratio (n = N/N A) between the number of elementary entities (N) and the Avogadro constant (N A). The entities are usually molecules, atoms, ions, or ion pairs of a specified kind.