Universal and Individual Gas Constants (2024)

The Universal and Individual Gas Constants in fluid mechanics and thermodynamics. Individual gas constants for the most common gases.

The Universal and Individual Gas Constants are known from the Ideal Gas Law .

The Individual Gas Constant - R

The Individual Gas Constant depends on the particular gas and is related to the molecular weight of the gas. The value is independent of temperature. The induvidual gas constant, R, for a gas can be calculated from the universal gas constant, R u ( given in several units below ), and the gas molecular weight, M gas :

R = R u /M gas [1]

In the imperial system the most common units for the individual gas constant are ft lb/slug o R . In the SI system the most common units are J/kg K .

Unit conversion: 1 J/kg K = 5.97994 ft lb/slug °R, and 1 ft lb/slug °R = 0.167226 J/kg K.

The Individual Gas Constant for gases:

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Individual Gas Constants
Gas Molecular
Weight
Individual Gas Constant - R
Name Formula [g/mol],
[kg/kmol]
[J/kg K] [kJ/kg K] [Wh/(kg K)] [kcal/(kg K)],
[Btu(IT)/lb °F]
[kcal/(lb °F)] [ft lbf /lb °R] [ft lbf /slug °R]
AcetyleneC2H 2 26.038 319.32 0.31930.088700.076270.062359.350 1910
Air A mixture 28.9647 287.05 0.28710.079740.068560.056053.353 1717
AmmoniaNH317.031 488.21 0.48820.135610.116610.095290.740 2919
ArgonAr39.948 208.13 0.20810.057810.049710.040638.684 1245
ButaneC 4 H 10 58.122 143.05 0.14310.039740.034170.027926.588 855
ButeneC 4 H 8 56.106 148.19 0.14820.041160.035390.028927.543 886
Carbon DioxideCO 2 44.010 188.92 0.18890.052480.045120.036835.114 1130
Carbon MonoxideCO28.010 296.84 0.29680.082460.070900.057955.171 1775
Carbonic acidH2CO362.025 134.05 0.13410.037240.032020.026124.915 802
ChlorineCl 2 70.906 117.26 0.11730.032570.028010.022921.794 701
ChloromethaneCH3Cl50.488 164.68 0.16470.045750.039330.032130.608 985
DichlorofluorumethaneCHCl2F102.923 80.78 0.08080.022440.019290.015815.015 483
EthaneC2H630.069 276.51 0.27650.076810.066040.053951.393 1654
EtheneC2H 4 28.053 296.38 0.29640.082330.070790.057855.086 1772
FluorineF 2 37.997 218.82 0.21880.060780.052260.042740.670 1309
HeliumHe4.003 2077.1 2.07710.576960.496100.4050386.047 12421
HydrogenH 2 2.016 4124.2 4.12421.145630.985060.8043766.541 24663
Hydrogen bromideHBr80.912 102.76 0.10280.028540.024540.020019.099 614
Hydrogen chlorideHCl36.461 228.04 0.22800.063340.054470.044542.384 1364
Hydrogen sulfideH2S34.081 243.96 0.24400.067770.058270.047645.344 1459
KryptonKr83.798 99.22 0.09920.027560.023700.019318.441 593
Methane (natural gas)CH 4 16.042 518.28 0.51830.143970.123790.101196.329 3099
NeonNe20.180 412.02 0.41200.114450.098410.080376.579 2464
NitrogenN 2 28.013 296.80 0.29680.082450.070890.057955.165 1775
Nitrogen dioxideNO 2 46.006 180.73 0.18070.050200.043170.035233.590 1081
Nitrogen trifluorideNF371.002 117.10 0.11710.032530.027970.022821.765 700
Nitrous oxideN2O44.012 188.91 0.18890.052480.045120.036835.112 1130
OxygenO 2 31.999 259.84 0.25980.072180.062060.050748.294 1554
PropaneC3 H 8 44.096 188.56 0.18860.052380.045040.036835.045 1128
PropeneC3 H642.080 197.59 0.19760.054890.047190.038536.724 1182
Sulfur dioxideSO 2 64.064 129.78 0.12980.036050.031000.025324.122 776
Sulfur hexafluorideSF6146.055 56.93 0.05690.015810.013600.011110.581 340
Sulfur trioxideSO380.063 103.85 0.10380.028850.024800.020319.302 621
Water vaporH2O18.015 461.52 0.46150.128200.110230.090085.780 2760
XenonXe131.293 63.33 0.06330.017590.015130.012311.770 379

The Universal Gas Constant - R u

The Universal Gas Constant - R u - appears in the ideal gas law and can be expressed as the product between the Individual Gas Constant - R - for the particular gas - and the Molecular Weight - M gas - for the gas, and is the same for all ideal or perfect gases :

R u = M gas R [2]

The Universal Constant defined in Terms of the Boltzmann's Constant

The universal gas constant can be defined in terms of Boltzmann's constant k as:

R u = k N A [3]

where
k = Boltzmann's constant = 1.381 x 10 -23 [J/K]
N A = Avogadro Number = 6.022 x 10 23 [1/mol]

The Molecular weight of a Gas Mixture

The average molecular weight of a gas mixture is equal to the sum of the mole fractions of each gas multiplied by the molecular weight of that particular gas:

M mixture = Σx i *M i = (x1 *M1 + ......+ x n *M n ) [4]

where

x i = mole fractions of each gas
M i = the molar mass of each gas

The Universal Gas Constant - R u - in alternative Units

  • atm.cm3 /(mol.K) : 82.057338
  • atm.ft3 /(lbmol.K) : 1.31443
  • atm.ft3 /(lbmol. o R) : 0.73024
  • atm.l/(mol.K) : 0.0820 57338
  • bar.cm3 /(mol.K) : 83.144598
  • bar.l/(mol.K) : 0.083144 598
  • Btu/(lbmol. o R) : 1.9872036
  • cal/(mol.K) : 1.9859
  • erg/(mol.K) : 83144 598
  • hp.h/(lbmol. o R) : 0.0007805
  • inHg.ft3 /(lbmol. o R) : 21.85
  • J/(mol.K) :8.3144598
  • kJ/(kmol.K) : 8.3144598
  • J/(kmol.K) : 8314.472
  • (kgf/cm2).l/(mol.K) : 0.084784
  • kPa.cm3 /(mol.K) : 8314.4 598
  • kWh/(lbmol. o R) : 0.000582
  • lbf.ft/(lbmol. o R) : 1545.349
  • mmHg.ft3 /(lbmol.K) : 999
  • mmHg.ft3 /(lbmol. o R) : 555
  • mmHg.l/(mol.K) : 62.363577
  • Pa.m3 /(mol.K) : 8.3144 598
  • psf.ft3 /(lbmol. o R) : 1545.3465
  • psi.ft3 /(lbmol. o R) : 10.73
  • Torr.cm3 /(mol.K) : 62364

See also:
- More material properties
- The Ideal Gas Law - Gases are highly compressible with changes in density directly related to changes in temperature and pressure.
- A Mixture of Gases - Properties of mixtures of gases.
- More about temperature

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