|Surname||Universal gas constant|
|SI||8th.314 462 618 153 24|
|Relation to other constants|
: Avogadro constant : Boltzmann constant
|Sources and Notes|
|Source SI value: CODATA 2018 ( direct link )|
The gas constant , also molar , universal or general gas constant, is a physical constant from thermodynamics . It occurs in the thermal equation of state of ideal gases . This equation establishes a relationship between pressure , volume , temperature and amount of substance of an ideal gas : The product of pressure and volume is proportional to the product of amount of substance and temperature. The ideal gas constant is the proportionality constant
Since the ideal gas equation can also be expressed with the number of particles instead of the amount of substance and the Boltzmann constant then appears as a constant of proportionality, there is a simple relationship between the gas constant, Boltzmann constant and the Avogadro constant , which links the number of particles and the amount of substance:
Since both constants have been given by definition since the revision of the International System of Units (SI) in 2019 , the numerical value of the gas constant is also exact:
The general gas constant was determined empirically . It is by no means obvious that the molar gas constant has the same value for all ideal gases and that there is thus a universal or general gas constant. One could assume that the gas pressure depends on the molecular mass of the gas, but this is not the case for ideal gases. Amadeo Avogadro first found in 1811 that the molar gas constant is the same for different ideal gases, known as Avogadro's Law .
The gas constant as the product of Avogadro and Boltzmann constants occurs in various areas of thermodynamics, mainly in the description of ideal gases. Such is the internal energy of ideal gases
and the molar heat capacity at constant pressure
Specific gas constant
in J kg −1 K −1
in g mol −1
|Argon , ar||208.1||39.95|
|Helium , he||2077.1||4.003|
|Carbon dioxide , CO 2||188.9||44.01|
|Carbon monoxide , CO||296.8||28.01|
|Methane , CH 4||518.4||16.04|
|Propane , C 3 H 8||188.5||44.10|
|Oxygen , O 2||259.8||32.00|
|Sulfur dioxide , SO 2||129.8||64.06|
|Nitrogen , N 2||296.8||28.01|
|Water vapor , H 2 O||461.4||18.02|
|Hydrogen , H 2||4124.2||2.016|
Example in air
The molar mass for dry air is 0.028 964 4 kg / mol. This results in the specific gas constant of air:
The thermal equation of state for ideal gases is then:
where m is the mass.
- The value is also exact as the product of two exact values, but in CODATA it is only given with the first ten valid digits, followed by periods. The numbers given in the info box are all valid.
- Wolfgang Demtröder: Experimentalphysik 1: Mechanics and heat . 6th edition. Springer, 2013, ISBN 978-3-642-25465-9 , pp. 266 .
- Langeheinecke: Thermodynamics for Engineers. Vieweg + Teubner, Wiesbaden 2008, ISBN 978-3-8348-0418-1
- Günter Warnecke: Meteorology and Environment: An Introduction. Google eBook, p. 14, limited preview in Google Book search.