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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 defines the number of constituent particles in one mole, where the particles in question can be either molecules, atoms, ions, ion pairs, or any other elementary entities.
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.
Avogadro's law states that "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules." [1] For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.
The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol R or R. It is the molar equivalent to the Boltzmann constant , expressed in units of energy per temperature increment per amount of substance , rather than energy per temperature increment per particle .
With the addition of Avogadro's law, the combined gas law develops into the ideal gas law: = where P is the pressure, V is volume, n is the number of moles, R is the universal gas constant and T is the absolute temperature.
In honour of Avogadro's contributions to molecular theory, the number of molecules per mole of a substance is named the Avogadro constant, N A. It is exactly 6.022 140 76 × 10 23 mol −1. [7] The Avogadro constant is used to compute the results of chemical reactions.
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).
Isotherms of an ideal gas for different temperatures. The curved lines are rectangular hyperbolae of the form y = a/x. They represent the relationship between pressure (on the vertical axis) and volume (on the horizontal axis) for an ideal gas at different temperatures: lines that are farther away from the origin (that is, lines that are nearer to the top right-hand corner of the diagram ...