Related Resources: thermodynamics

Van der Waals Constants for Gases

Engineering Materials Specifications and Characteristics Tables and Charts
Thermodynamics and Heat Transfer

Van der Waals Constants for Gases

Van der Waals, constant a is due to force of attraction and b due to the infinite size molecules. The greater the value q and smaller the value b, larger the liquefaction.

The formula for Van der Waals equation of state for a real gas is:

(P + n2a/V2)(V -nb) = nRT

where:

P is the pressure,
V the volume,
T the temperature,
n the amount of substance (in moles),
R the gas constant.

Van der Waals equation

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 = 27R2Tc2/64Pcb = RTc /8Pc

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.

Substance
a
b
bar L2/mol2
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
b
bar L2/mol2
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

Reference:

Reid, R.C, Prausnitz, J. M., and Poling, B.E., The Properties of Gases and Liquids, Fourth Edition, McGraw-Hill, New York, 1987.

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