Van der Waals Constants for Gases
The van der Waals equation of state for a real gas is
	 ( / )( – )P n a V V nb nRT+ =2 2
where P is the pressure, V the volume, T the temperature, n the
amount of substance (in moles), and R the gas constant. The van
der Waals constants a and b are characteristic of the substance and
are independent of temperature. They are related to the critical
temperature and pressure, Tc
and Pc
, by
	 a R T P b RT Pc c c c
= =27 64 82 2
/ /
This table gives values of a and b for some common gases. Most
of the values have been calculated from the critical temperature
and pressure values given in the table “Critical Constants” in this
section. Van der Waals constants for other gases may easily be calculated
from the data in that table.
To convert the van der Waals constants to SI units, note that 1
bar L2
/mol2
= 0.1 Pa m6
/mol2
and 1 L/mol = 0.001 m3
/mol.
Reference
Reid, R. C, Prausnitz, J. M., and Poling, B. E., The Properties of Gases and
Liquids, Fourth Edition, McGraw-Hill, New York, 1987.
Substance
a
bar L2
/mol2
b
L/mol
Acetic acid 17.71 0.1065
Acetone 16.02 0.1124
Acetylene 4.516 0.0522
Ammonia 4.225 0.0371
Aniline 29.14 0.1486
Argon 1.355 0.0320
Benzene 18.82 0.1193
Bromine 9.75 0.0591
Butane 13.89 0.1164
1-Butanol 20.94 0.1326
2-Butanone 19.97 0.1326
Carbon dioxide 3.658 0.0429
Carbon disulfide 11.25 0.0726
Carbon monoxide 1.472 0.0395
Chlorine 6.343 0.0542
Chlorobenzene 25.80 0.1454
Chloroethane 11.66 0.0903
Chloromethane 7.566 0.0648
Cyclohexane 21.92 0.1411
Cyclopropane 8.34 0.0747
Decane 52.74 0.3043
1-Decanol 59.51 0.3086
Diethyl ether 17.46 0.1333
Dimethyl ether 8.690 0.0774
Dodecane 69.38 0.3758
1-Dodecanol 75.70 0.3750
Ethane 5.580 0.0651
Ethanol 12.56 0.0871
Ethylene 4.612 0.0582
Fluorine 1.171 0.0290
Furan 12.74 0.0926
Helium 0.0346 0.0238
Heptane 31.06 0.2049
1-Heptanol 38.17 0.2150
Hexane 24.84 0.1744
1-Hexanol 31.79 0.1856
Hydrazine 8.46 0.0462
Hydrogen 0.2452 0.0265
Hydrogen bromide 4.500 0.0442
Hydrogen chloride 3.700 0.0406
Hydrogen cyanide 11.29 0.0881
Hydrogen fluoride 9.565 0.0739
Hydrogen iodide 6.309 0.0530
Substance
a
bar L2
/mol2
b
L/mol
Hydrogen sulfide 4.544 0.0434
Isobutane 13.32 0.1164
Krypton 5.193 0.0106
Methane 2.303 0.0431
Methanol 9.476 0.0659
Methylamine 7.106 0.0588
Neon 0.208 0.0167
Neopentane 17.17 0.1411
Nitric oxide 1.46 0.0289
Nitrogen 1.370 0.0387
Nitrogen dioxide 5.36 0.0443
Nitrogen trifluoride 3.58 0.0545
Nitrous oxide 3.852 0.0444
Octane 37.88 0.2374
1-Octanol 44.71 0.2442
Oxygen 1.382 0.0319
Ozone 3.570 0.0487
Pentane 19.09 0.1449
1-Pentanol 25.88 0.1568
Phenol 22.93 0.1177
Propane 9.39 0.0905
1-Propanol 16.26 0.1079
2-Propanol 15.82 0.1109
Propene 8.442 0.0824
Pyridine 19.77 0.1137
Pyrrole 18.82 0.1049
Silane 4.38 0.0579
Sulfur dioxide 6.865 0.0568
Sulfur hexafluoride 7.857 0.0879
Tetrachloromethane 20.01 0.1281
Tetrachlorosilane 20.96 0.1470
Tetrafluoroethylene 6.954 0.0809
Tetrafluoromethane 4.040 0.0633
Tetrafluorosilane 5.259 0.0724
Tetrahydrofuran 16.39 0.1082
Thiophene 17.21 0.1058
Toluene 24.86 0.1497
1,1,1-Trichloroethane 20.15 0.1317
Trichloromethane 15.34 0.1019
Trifluoromethane 5.378 0.0640
Trimethylamine 13.37 0.1101
Water 5.537 0.0305
Xenon 4.192 0.0516
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