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# Universal and Individual Gas Constants

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:

For full table - rotate the screen!

 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 lb f /lb °R] [ft lb f /slug °R] Acetylene C 2 H 2 26.038 319.32 0.3193 0.08870 0.07627 0.0623 59.350 1910 Air A mixture 28.9647 287.05 0.2871 0.07974 0.06856 0.0560 53.353 1717 Ammonia NH 3 17.031 488.21 0.4882 0.13561 0.11661 0.0952 90.740 2919 Argon Ar 39.948 208.13 0.2081 0.05781 0.04971 0.0406 38.684 1245 Butane C 4 H 10 58.122 143.05 0.1431 0.03974 0.03417 0.0279 26.588 855 Butene C 4 H 8 56.106 148.19 0.1482 0.04116 0.03539 0.0289 27.543 886 Carbon Dioxide CO 2 44.010 188.92 0.1889 0.05248 0.04512 0.0368 35.114 1130 Carbon Monoxide CO 28.010 296.84 0.2968 0.08246 0.07090 0.0579 55.171 1775 Carbonic acid H 2 CO 3 62.025 134.05 0.1341 0.03724 0.03202 0.0261 24.915 802 Chlorine Cl 2 70.906 117.26 0.1173 0.03257 0.02801 0.0229 21.794 701 Chloromethane CH3Cl 50.488 164.68 0.1647 0.04575 0.03933 0.0321 30.608 985 Dichlorofluorumethane CHCl2F 102.923 80.78 0.0808 0.02244 0.01929 0.0158 15.015 483 Ethane C 2 H 6 30.069 276.51 0.2765 0.07681 0.06604 0.0539 51.393 1654 Ethene C 2 H 4 28.053 296.38 0.2964 0.08233 0.07079 0.0578 55.086 1772 Fluorine F 2 37.997 218.82 0.2188 0.06078 0.05226 0.0427 40.670 1309 Helium He 4.003 2077.1 2.0771 0.57696 0.49610 0.4050 386.047 12421 Hydrogen H 2 2.016 4124.2 4.1242 1.14563 0.98506 0.8043 766.541 24663 Hydrogen bromide HBr 80.912 102.76 0.1028 0.02854 0.02454 0.0200 19.099 614 Hydrogen chloride HCl 36.461 228.04 0.2280 0.06334 0.05447 0.0445 42.384 1364 Hydrogen sulfide H2S 34.081 243.96 0.2440 0.06777 0.05827 0.0476 45.344 1459 Krypton Kr 83.798 99.22 0.0992 0.02756 0.02370 0.0193 18.441 593 Methane (natural gas) CH 4 16.042 518.28 0.5183 0.14397 0.12379 0.1011 96.329 3099 Neon Ne 20.180 412.02 0.4120 0.11445 0.09841 0.0803 76.579 2464 Nitrogen N 2 28.013 296.80 0.2968 0.08245 0.07089 0.0579 55.165 1775 Nitrogen dioxide NO 2 46.006 180.73 0.1807 0.05020 0.04317 0.0352 33.590 1081 Nitrogen trifluoride NF 3 71.002 117.10 0.1171 0.03253 0.02797 0.0228 21.765 700 Nitrous oxide N 2 O 44.012 188.91 0.1889 0.05248 0.04512 0.0368 35.112 1130 Oxygen O 2 31.999 259.84 0.2598 0.07218 0.06206 0.0507 48.294 1554 Propane C 3 H 8 44.096 188.56 0.1886 0.05238 0.04504 0.0368 35.045 1128 Propene C 3 H 6 42.080 197.59 0.1976 0.05489 0.04719 0.0385 36.724 1182 Sulfur dioxide SO 2 64.064 129.78 0.1298 0.03605 0.03100 0.0253 24.122 776 Sulfur hexafluoride SF 6 146.055 56.93 0.0569 0.01581 0.01360 0.0111 10.581 340 Sulfur trioxide SO 3 80.063 103.85 0.1038 0.02885 0.02480 0.0203 19.302 621 Water vapor H 2 O 18.015 461.52 0.4615 0.12820 0.11023 0.0900 85.780 2760 Xenon Xe 131.293 63.33 0.0633 0.01759 0.01513 0.0123 11.770 379

### 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 = (x 1 *M 1 + ......+ 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.cm 3 /(mol.K) : 82.057338
• atm.ft 3 /(lbmol.K) : 1.31443
• atm.ft 3 /(lbmol. o R) : 0.73024
• atm.l/(mol.K) : 0.0820 57338
• bar.cm 3 /(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.ft 3 /(lbmol. o R) :  21.85
• J/(mol.K) :  8.3144598
• kJ/(kmol.K) :  8.3144598
• J/(kmol.K) : 8314.472
• (kgf/cm 2 ).l/(mol.K) : 0.084784
• kPa.cm 3 /(mol.K) : 8314.4 598
• kWh/(lbmol. o R) : 0.000582
• lbf.ft/(lbmol. o R) : 1545.349
• mmHg.ft 3 /(lbmol.K) : 999
• mmHg.ft 3 /(lbmol. o R) : 555
• mmHg.l/(mol.K) : 62.363577
• Pa.m 3 /(mol.K) : 8.3144 598
• psf.ft 3 /(lbmol. o R) : 1545.3465
• psi.ft 3 /(lbmol. o R) : 10.73
• Torr.cm 3 /(mol.K) : 62364

- 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.

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