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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.

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
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
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

* 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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