Gas constant

Thus, the value of the gas constant ultimately derives from historical decisions and accidents in the setting of units of energy, temperature and amount of substance.

The universal gas constant was apparently introduced independently by August Friedrich Horstmann (1873)[3][4] and Dmitri Mendeleev who reported it first on 12 September 1874.

[5] Using his extensive measurements of the properties of gases,[6][7] Mendeleev also calculated it with high precision, within 0.3% of its modern value.

where P is the absolute pressure, V is the volume of gas, n is the amount of substance, m is the mass, and T is the thermodynamic temperature.

From the ideal gas law PV = nRT we get: where P is pressure, V is volume, n is number of moles of a given substance, and T is temperature.

It may be expressed in any set of units representing work or energy (such as joules), units representing degrees of temperature on an absolute scale (such as kelvin or rankine), and any system of units designating a mole or a similar pure number that allows an equation of macroscopic mass and fundamental particle numbers in a system, such as an ideal gas (see Avogadro constant).

Finally, by defining the kinetic energy associated to the temperature: the equation becomes simply: which is the form usually encountered in statistical mechanics and other branches of theoretical physics.

[13] This disparity is not a significant departure from accuracy, and USSA1976 uses this value of R∗ for all the calculations of the standard atmosphere.