Gas constant

The universal, ideal, or even molar gas constant ( symbols: R, Rm or Rn) is the product of Avogadro's constant ( NA) and the Boltzmann constant ( kB):

The gas constant, has the value:

(that is, with an estimated standard deviation of 0.000 007 5 J mol -1 K-1).

The universal gas constant was empirically as proportional constant of the general gas equation

Determined and serves the combination of the properties temperature (T), molar (s ), pressure (P) and volume (V), but is also used in numerous other applications and formulas.

However, it is far from obvious here, that the molar gas constant for all ideal gases has the same value, and that there is a universal or general gas constant in sequence. It could be assumed that the gas pressure is dependent on the molecular weight of the gas, which, however, for ideal gases is not the case. The finding that the molar gas constant is identical for different ideal gases it follows from the law of Avogadro, which was first postulated in 1811 by Amadeo Avogadro.

The product of the amount of substance and general gas constant was formerly called Regnaultsche number or Regnaultsche constant ( after Henri Victor Regnault ).

Specific gas constant

The universal gas constant divided by the molar mass of a gas results in the specific or even individual gas constant (symbol: Rs, Ri, Rspez )

Since the molecular weight is usually the more common characteristic of a gas, the use of the specific gas constant should be avoided and, instead, is the universal gas constant can be used together with the molecular weight.

Example of air

The molar mass for dry air is 0.028 964 4 kg / mol. Thus, for the specific gas constant of air: