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Non-ideal gas - Van der Waal's Equation and Constants

The van der Waals constants for more than 200 gases used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles.

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The ideal gas law treats the molecules of a gas as point particles with perfectly elastic collisions. This works well for dilute gases in many experimental circumstances.

However,  gas molecules are not point masses, and there are many cases gases need to be treated as non-ideal.  Johannes D. van der Waals suggested a modification to take into account molecular size and molecular interaction forces. It is usually referred to as the van der Waals equation of state:

[P + a(n/V)2] (V/n - b) = RT

The constants a and b are called  van der Waals constants. They have positive values and are characteristic of the individual gas. If a gas behaves ideally, both a and b are zero, and van der Waals equations approaches the ideal gas law PV=nRT. 

The constant a provides a correction for the intermolecular forces.
Constant b adjusts for the volume occupied by the gas particles. It is a correction for finite molecular size and its value is the volume of one mole of the atoms or molecules.

See also the Gas Compressibility Factor, z-factor for air, dependent on pressure and temperature and used to account for deviation from the ideal situation.
How to calculate total pressure and partial pressures from Ideal gas law

* To convert a into atm L2/mol2 multiply by 0.986 atm/bar.    To convert a into kPa L2/mol2 multiply by 100.0 kPa/bar

NameMolecular Formulaa*
bar L2/mol2		b
L/mol
  Aluminum trichloride AlCl3 42.63 0.245
  Ammonia NH3 4.225 0.03713
  Ammonium chloride NH4Cl 2.38 0.00734
  Argon Ar 1.355 0.03201
  Boron trichloride BCl3 15.6 0.1222
  Boron trifluoride BF3 3.98 0.05443
  Diborane B2H6 6.048 0.07437
  Bromine Br2 9.75 0.0591
  Perchloryl fluoride ClFO2 7.371 0.0713
  Chlorine pentafluoride ClF5 9.58 0.08204
  Phosphonium chloride ClH4P 4.111 0.04545
  Chlorine Cl2 6.343 0.05422
  Trichlorofluorosilane Cl3FSi 15.67 0.1273
  Fluorine F2 1.171 0.02896
  Germanium tetrachloride GeCl4 23.12 0.1489
  Nitrogen trifluoride F3N 3.58 0.05453
  Phosphorus trifluoride F3P 4.954 0.0651
  Tetrafluorohydrazine F4N2 7.426 0.08564
  Germane GeH4 5.743 0.06555
  Helium He 0.0346 0.0238
  Hydrogen bromide HBr 4.5 0.04415
  Hydrogen chloride HCl 3.7 0.04061
  Hydrogen cyanide HCN 11.29 0.08806
  Hydrogen fluoride HF 9.565 0.0739
  Hydrogen iodide HI 6.309 0.05303
  Hydrogen H2 0.2453 0.02651
  Water H2O 5.537 0.03049
  Hydrogen sulphide H2S 4.544 0.04339
  Hydrogen selenide H2Se 5.523 0.0479
  Krypton Kr 2.325 0.0396
  Silane SiH4 4.38 0.0579
  Silicon tetrachloride SiCl4 20.96 0.147
  Silicon tetrafluoride SiF4 5.259 0.07236
  Titanium(IV) chloride TiCl4 25.47 0.1423
  Mercury Hg 5.193 0.01057
  Nitric oxide NO 1.46 0.0289
  Nitrogen dioxide NO2 5.36 0.0443
  Nitrogen N2 1.37 0.0387
  Nitrous oxide N2O 3.852 0.04435
  Hydrazine N2H4 8.46 0.0462
  Neon Ne 0.208 0.01672
  Oxygen O2 1.382 0.03186
  Ozone O3 3.57 0.0487
  Phosphorus P 53.6 0.157
  Phosphine PH3 4.696 0.05157
  Radon Rn 6.601 0.06239
  Stannic chloride SnCl4 27.25 0.1641
  Sulphur S 24.3 0.066
  Sulphur dioxide SO2 6.865 0.05679
  Sulphur hexafluoride SF6 7.857 0.08786
  Selenium Se 33.4 0.0675
  Uranium(VI) fluoride UF6 16.01 0.1128
  Tungsten(VI) fluoride WF6 13.25 0.1063
  Xenon Xe 4.192 0.05156
  Xenon difluoride XeF2 12.46 0.07037
  Xenon tetrafluoride XeF4 15.52 0.09035
  Chlorotrifluoromethane CClF3 6.873 0.0811
  Trichlorofluoromethane CCl3F 14.68 0.1111
  Tetrachloromethane CCl4 20.01 0.1281
  Tetrafluoromethane CF4 4.04 0.06325
  Carbon monoxide CO 1.472 0.03948
  Carbon oxysulphide COS 6.975 0.06628
  Carbon dioxide CO2 3.658 0.04286
  Carbon disulphide CS2 11.25 0.07262
  Trichloromethane CHCl3 15.34 0.1019
  Trifluoromethane CHF3 5.378 0.06403
  Dichloromethane CH2Cl2 12.44 0.08689
  Difluoromethane CH2F2 6.184 0.06268
  Chloromethane CH3Cl 7.566 0.06477
  Fluoromethane CH3F 5.009 0.05617
  Nitromethane NH3NO2 17.18 0.1041
  Methane CH4 2.3 0.04301
  Methanol CH3OH 9.472 0.06584
  Methanethiol CH3SH 8.911 0.06756
  Methylamine CH3NH2 7.106 0.05879
  1,1,2-Trichlorotrifluoroethane C2Cl2F3 20.25 0.1481
  Tetrafluoroethylene C2F4 6.954 0.08085
  Cyanogen C2N2 7.803 0.6952
  Acetylene C2H2 4.516 0.0522
  1,1-Difluoroethylene C2H2F2 6 0.07058
  1,1,1-Trichloroethane C2H3Cl3 20.15 0.1317
  Fluroethylene C2H3F 5.984 0.06504
  1,1,1-Trifluoroethane C2H3F3 9.302 0.09572
  Acetonitrile C2H3N 17.89 0.1169
  Ethylene C2H4 4.612 0.05821
  1,1-Dichloroethane C2H4Cl2 15.73 0.1072
  1,2-Dichloroethane C2H4Cl2 17 0.108
  Ethylene oxide C2H4O 8.922 0.06779
  Acetic acid CH3COOH 17.71 0.1065
  Methyl formate C2H4O2 11.54 0.08442
  Bromoethane C2H5Br 11.89 0.08406
  Chloroethane C2H5Cl 11.7 0.09
  Fluoroethane C2H5F 8.17 0.07758
  Ethane C2H6 5.57 0.06499
  Dimethyl ether C2H6O 8.69 0.07742
  Ethanol C2H5OH 12.56 0.0871
  Dimethyl sulphide C2H5SH 13.34 0.09453
  Ethanethiol C2H5SH 13.23 0.09447
  Dimethylamine C2H7N 10.44 0.0851
  Ethylamine C2H7N 10.79 0.08433
  Perfluoropropane C3F8 12.96 0.1338
  Propanenitrile C3H5N 21.57 0.1369
  Propene C3H6 8.438 0.08242
  Cyclopropane C3H6 8.293 0.0742
  Acetone C3H6O 16.02 0.1124
  Propanal C3H6O 14.08 0.09947
  Ethyl formate C3H6O2 15.91 0.1115
  Methyl acetate C3H6O2 15.75 0.1108
  Propanoic acid C3H6O2 23.49 0.1386
  1-Chloropropane C3H7Cl 16.11 0.1141`
  Propane C3H8 9.385 0.09044
  1-Propanol C3H8O 16.26 0.108
  2-Propanol C3H8O 15.82 0.1109
  Ethyl methyl ether C3H8O 12.7 0.1034
  Ethyl methyl sulphide C3H8S 19.45 0.13
  Propylamine C3H9N 15.26 0.1094
  Trimethylamine C3H9N 13.37 0.1101
  Furan C4H4O 12.74 0.0926
  Thiophene C4H4S 17.21 0.1058
  Pyrrole C4H4N 18.82 0.1049
  1,3-Butadiene C4H6 12.17 0.102
  Acetic anhydride C4H6O3 26.8 0.157
  Butanenitrile C4H7N 25.76 0.1568
  1-Butene C4H8 12.76 0.1084
  Cyclobutane C4H8 12.39 0.096
  2-Butanone C4H8O 19.97 0.1326
  Tetrahydrofuran C4H8O 16.39 0.1082
  1,4-Dioxane C4H8O2 19.29 0.1171
  Ethyl acetate C4H8O2 20.57 0.1401
  Methyl propanoate C4H8O2 20.51 0.1377
  Propyl formate C4H8O2 20.79 0.1377
  Butanoic acid C4H8O2 28.18 0.1609
  Pyrrolidine C4H9N 16.84 0.1056
  Butane C4H10 13.93 0.1168
  Isobutane C4H10 13.36 0.1168
  1-Butanol C4H10O 20.9 0.1323
  2-Methyl-2-propanol C4H10O 18.81 0.1324
  2-Methyl-1-propanol C4H10O 20.35 0.1324
  Diethyl ether C4H10O 17.46 0.1333
  Diethyl sulphide C4H10S 22.85 0.1462
  Butylamine C4H11N 19.41 0.1301
  Diethylamine C4H11N 19.4 0.1383
  Tetramethylsilane C4H12Si 20.81 0.1653
  Furfural C5H4O2 22.23 0.1182
  Pyridine C5H5N 19.77 0.1137
  Cyclopentene C5H8 15.61 0.1097
  1-Pentene C5H10 17.86 0.137
  2-Methyl-1-butene C5H10 16.9 0.129
  2-Methyl-2-butene C5H10 17.26 0.1279
  Cyclopentane C5H10 16.94 0.118
  Tetrahydropyran C5H10O 20.02 0.1247
  Isobutyl formate C5H10O2 22.82 0.1476
  Propyl acetate C5H10O2 26.23 0.17
  Ethyl propanoate C5H10O2 25.86 0.1688
  Methyl butanoate C5H10O2 25.83 0.1661
  Methyl isobutanoate C5H10O2 24.87 0.1639
  Piperidine C5H11N 20.84 0.125
  Pentane C5H12 19.13 0.1451
  Isopentane C5H12 18.29 0.1415
  Neopentane C5H12 17.17 0.141
  1-Pentanol C5H12O 25.81 0.1564
  Bromobenzene C6H5Br 28.96 0.1541
  Chlorobenzene C6H5Cl 25.8 0.1454
  Fluorobenzene C6H5F 20.1 0.1279
  Iodobenzene C6H5I 33.54 0.1658
  Benzene C6H6 18.82 0.1193
  Phenol C6H5OH 22.93 0.1177
  Aniline C6H5NH2 29.14 0.1486
  Cyclohexanone C6H10O 31.1 0.17
  Hexanenitrile C6H11N 35.5 0.1996
  Cyclohexane C6H12 21.95 0.1413
  Cyclohexanol C6H11OH 28.93 0.1586
  Pentyl formate C6H12O2 27.97 0.173
  Isobutyl acetate C6H12O2 29.05 0.1845
  Ethyl butanoate C6H12O2 30.53 0.1922
  Ethyl 2-methylpropanoate C6H12O2 29.05 0.1872
  Methyl pentanoate C6H12O2 29.39 0.1847
  Hexane C6H14 24.97 0.1753
  2,3-Dimethylbutane C6H14 23.29 0.166
  1-Hexanol C6H14O 31.35 0.1829
  Triethylamine C6H15N 27.59 0.1836
  Dipropylamine C6H15N 24.82 0.1591
  Benzonitrile C7H5N 33.89 0.1727
  Benzaldehyde C7H6O 30.3 0.1553
  Toluene C7H8 24.89 0.1499
  o-Cresol C7H8O 28.33 0.1447
  m-Cresol C7H8O 31.86 0.1609
  p-Cresol C7H8O 28.11 0.1422
  Benzyl alcohol C7H8O 34.7 0.173
  Anisole C7H8O 28.6 0.1579
  Heptane C7H16 30.89 0.2038
  Heptanol C7H15OH 37.22 0.2097
  Ethylbenzene C8H10 30.86 0.1782
  o-Xylene C8H10 31.06 0.1756
  m-Xylene C8H10 31.41 0.1814
  p-Xylene C8H10 31.54 0.1824
  Phenetole C8H10O 35.7 0.1966
  N,N-Dimethylaniline C8H11N 37.92 0.1967
  Octane C8H18 37.86 0.2372
  2,5-Dimethylhexane C8H18 35.49 0.2299
  1-Octanol C8H18O 43.42 0.2371
  Quinoline C9H7N 36.7 0.1672
  Cumene C9H12 36.2 0.2044
  Propylbenzene C9H12 37.14 0.2073
  1,2,4-Trimethylbenzene C9H12 38.03 0.2088
  Mesitylene C9H12 37.87 0.2118
  Nonane C9H20 45.11 0.2702
  1-Nonanol C9H20O 50 0.2654
  Naphthalene C10H8 40.32 0.192
  Butylbenzene C10H14 44.07 0.2378
  Isobutylbenzene C10H14 40.4 0.2215
  o-Cymene C10H14 42.7 0.234
  p-Cymene C10H14 45.27 0.2478
  p-Diethylbenzene C10H14 45.03 0.2439
  1,2,4,5-Tetramethylbenzene C10H14 45.8 0.24
  Decane C10H22 52.88 0.3051
  1-Decanol C10H22O 57.45 0.2971
  Undecane C11H24 60.88 0.3396
  Biphenyl C12H10 47.16 0.213
  Dodecane C12H26 69.14 0.3741
  1-Dodecanol C12H26O 72.69 0.3598
  Diphenylmethane C13H12 60.46 0.2798
  Tridecane C13H28 77.94 0.4109
  1-Tridecanol C13H28O 81.2 0.3942
  1-Tetradecanol C14H30O 89.91 0.4289
  Pentadecane C15H32 96.5 0.4857

* To convert a into atm L2/mol2 multiply by 0.986 atm/bar

 * To convert a into kPa L2/mol2 multiply by 100.0 kPa/bar

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