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) = R T (1)

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 P V = n R T.

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/mol²multiply by 0.986 atm/bar. To convert a into kPa L²/mol²multiply by 100.0 kPa/bar.

Non-ideal gas - Van der Waal's Constants
Name	Molecular Formula	a* bar L²/mol²	b L/mol
Aluminum trichloride	AlCl₃	42.63	0.245
Ammonia	NH₃	4.225	0.03713
Ammonium chloride	NH₄ Cl	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	ClH₄ P	4.111	0.04545
Chlorine	Cl₂	6.343	0.05422
Trichlorofluorosilane	Cl₃ FSi	15.67	0.1273
Fluorine	F₂	1.171	0.02896
Germanium tetrachloride	GeCl₄	23.12	0.1489
Nitrogen trifluoride	F₃ N	3.58	0.05453
Phosphorus trifluoride	F₃ P	4.954	0.0651
Tetrafluorohydrazine	F₄ N₂	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	CCl₃ F	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	CH₃ Cl	7.566	0.06477
Fluoromethane	CH3F	5.009	0.05617
Nitromethane	NH₃ NO₂	17.18	0.1041
Methane	CH₄	2.3	0.04301
Methanol	CH₃ OH	9.472	0.06584
Methanethiol	CH₃ SH	8.911	0.06756
Methylamine	CH₃ NH₂	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	C₂H₃ Cl₃	20.15	0.1317
Fluroethylene	C₂H₃ F	5.984	0.06504
1,1,1-Trifluoroethane	C₂H₃ F₃	9.302	0.09572
Acetonitrile	C₂H₃ N	17.89	0.1169
Ethylene	C₂H₄	4.612	0.05821
1,1-Dichloroethane	C₂H₄ Cl₂	15.73	0.1072
1,2-Dichloroethane	C₂H₄ Cl₂	17	0.108
Ethylene oxide	C₂H₄ O	8.922	0.06779
Acetic acid	CH₃ COOH	17.71	0.1065
Methyl formate	C₂H₄ O₂	11.54	0.08442
Bromoethane	C₂H₅ Br	11.89	0.08406
Chloroethane	C₂H₅ Cl	11.7	0.09
Fluoroethane	C₂H₅ F	8.17	0.07758
Ethane	C₂H₆	5.57	0.06499
Dimethyl ether	C₂H₆ O	8.69	0.07742
Ethanol	C₂H₅ OH	12.56	0.0871
Dimethyl sulphide	C₂H₅ SH	13.34	0.09453
Ethanethiol	C₂H₅ SH	13.23	0.09447
Dimethylamine	C₂H₇ N	10.44	0.0851
Ethylamine	C₂H₇ N	10.79	0.08433
Perfluoropropane	C₃ F₈	12.96	0.1338
Propanenitrile	C₃ H₅ N	21.57	0.1369
Propene	C₃ H₆	8.438	0.08242
Cyclopropane	C₃ H₆	8.293	0.0742
Acetone	C₃ H₆ O	16.02	0.1124
Propanal	C₃ H₆ O	14.08	0.09947
Ethyl formate	C₃ H₆ O₂	15.91	0.1115
Methyl acetate	C₃ H₆ O₂	15.75	0.1108
Propanoic acid	C₃ H₆ O₂	23.49	0.1386
1-Chloropropane	C₃ H₇ Cl	16.11	0.1141`
Propane	C₃ H₈	9.385	0.09044
1-Propanol	C₃ H₈ O	16.26	0.108
2-Propanol	C₃ H₈ O	15.82	0.1109
Ethyl methyl ether	C₃ H₈ O	12.7	0.1034
Ethyl methyl sulphide	C₃ H₈ S	19.45	0.13
Propylamine	C₃ H₉ N	15.26	0.1094
Trimethylamine	C₃ H₉ N	13.37	0.1101
Furan	C₄ H₄ O	12.74	0.0926
Thiophene	C₄ H₄ S	17.21	0.1058
Pyrrole	C₄ H₄ N	18.82	0.1049
1,3-Butadiene	C₄ H₆	12.17	0.102
Acetic anhydride	C₄ H₆ O₃	26.8	0.157
Butanenitrile	C₄ H₇ N	25.76	0.1568
1-Butene	C₄ H₈	12.76	0.1084
Cyclobutane	C₄ H₈	12.39	0.096
2-Butanone	C₄ H₈ O	19.97	0.1326
Tetrahydrofuran	C₄ H₈ O	16.39	0.1082
1,4-Dioxane	C₄ H₈ O₂	19.29	0.1171
Ethyl acetate	C₄ H₈ O₂	20.57	0.1401
Methyl propanoate	C₄ H₈ O₂	20.51	0.1377
Propyl formate	C₄ H₈ O₂	20.79	0.1377
Butanoic acid	C₄ H₈ O₂	28.18	0.1609
Pyrrolidine	C₄ H₉ N	16.84	0.1056
Butane	C₄ H₁₀	13.93	0.1168
Isobutane	C₄ H₁₀	13.36	0.1168
1-Butanol	C₄ H₁₀ O	20.9	0.1323
2-Methyl-2-propanol	C₄ H₁₀ O	18.81	0.1324
2-Methyl-1-propanol	C₄ H₁₀ O	20.35	0.1324
Diethyl ether	C₄ H₁₀ O	17.46	0.1333
Diethyl sulphide	C₄ H₁₀ S	22.85	0.1462
Butylamine	C₄ H₁₁ N	19.41	0.1301
Diethylamine	C₄ H₁₁ N	19.4	0.1383
Tetramethylsilane	C₄ H₁₂ Si	20.81	0.1653
Furfural	C₅ H₄ O₂	22.23	0.1182
Pyridine	C₅ H₅ N	19.77	0.1137
Cyclopentene	C₅ H₈	15.61	0.1097
1-Pentene	C₅ H₁₀	17.86	0.137
2-Methyl-1-butene	C₅ H₁₀	16.9	0.129
2-Methyl-2-butene	C₅ H₁₀	17.26	0.1279
Cyclopentane	C₅ H₁₀	16.94	0.118
Tetrahydropyran	C₅ H₁₀ O	20.02	0.1247
Isobutyl formate	C₅ H₁₀ O₂	22.82	0.1476
Propyl acetate	C₅ H₁₀ O₂	26.23	0.17
Ethyl propanoate	C₅ H₁₀ O₂	25.86	0.1688
Methyl butanoate	C₅ H₁₀ O₂	25.83	0.1661
Methyl isobutanoate	C₅ H₁₀ O₂	24.87	0.1639
Piperidine	C₅ H₁₁ N	20.84	0.125
Pentane	C₅ H₁₂	19.13	0.1451
Isopentane	C₅ H₁₂	18.29	0.1415
Neopentane	C₅ H₁₂	17.17	0.141
1-Pentanol	C₅ H₁₂ O	25.81	0.1564
Bromobenzene	C₆ H₅ Br	28.96	0.1541
Chlorobenzene	C₆ H₅ Cl	25.8	0.1454
Fluorobenzene	C₆ H₅ F	20.1	0.1279
Iodobenzene	C₆ H₅ I	33.54	0.1658
Benzene	C₆ H₆	18.82	0.1193
Phenol	C₆ H₅ OH	22.93	0.1177
Aniline	C₆ H₅ NH₂	29.14	0.1486
Cyclohexanone	C₆ H₁₀ O	31.1	0.17
Hexanenitrile	C₆ H₁₁ N	35.5	0.1996
Cyclohexane	C₆ H₁₂	21.95	0.1413
Cyclohexanol	C₆ H₁₁ OH	28.93	0.1586
Pentyl formate	C₆ H₁₂ O₂	27.97	0.173
Isobutyl acetate	C₆ H₁₂ O₂	29.05	0.1845
Ethyl butanoate	C₆ H₁₂ O₂	30.53	0.1922
Ethyl 2-methylpropanoate	C₆ H₁₂ O₂	29.05	0.1872
Methyl pentanoate	C₆ H₁₂ O₂	29.39	0.1847
Hexane	C₆ H₁₄	24.97	0.1753
2,3-Dimethylbutane	C₆ H₁₄	23.29	0.166
1-Hexanol	C₆ H₁₄ O	31.35	0.1829
Triethylamine	C₆ H₁₅ N	27.59	0.1836
Dipropylamine	C₆ H₁₅ N	24.82	0.1591
Benzonitrile	C₇ H₅ N	33.89	0.1727
Benzaldehyde	C₇ H₆ O	30.3	0.1553
Toluene	C₇ H₈	24.89	0.1499
o-Cresol	C₇ H₈ O	28.33	0.1447
m-Cresol	C₇ H₈ O	31.86	0.1609
p-Cresol	C₇ H₈ O	28.11	0.1422
Benzyl alcohol	C₇ H₈ O	34.7	0.173
Anisole	C₇ H₈ O	28.6	0.1579
Heptane	C₇ H₁₆	30.89	0.2038
Heptanol	C₇ H₁₅ OH	37.22	0.2097
Ethylbenzene	C₈ H₁₀	30.86	0.1782
o-Xylene	C₈ H₁₀	31.06	0.1756
m-Xylene	C₈ H₁₀	31.41	0.1814
p-Xylene	C₈ H₁₀	31.54	0.1824
Phenetole	C₈ H₁₀ O	35.7	0.1966
N,N-Dimethylaniline	C₈ H₁₁ N	37.92	0.1967
Octane	C₈ H₁₈	37.86	0.2372
2,5-Dimethylhexane	C₈ H₁₈	35.49	0.2299
1-Octanol	C₈ H₁₈ O	43.42	0.2371
Quinoline	C₉ H₇ N	36.7	0.1672
Cumene	C₉ H₁₂	36.2	0.2044
Propylbenzene	C₉ H₁₂	37.14	0.2073
1,2,4-Trimethylbenzene	C₉ H₁₂	38.03	0.2088
Mesitylene	C₉ H₁₂	37.87	0.2118
Nonane	C₉ H₂₀	45.11	0.2702
1-Nonanol	C₉ H₂₀ O	50	0.2654
Naphthalene	C₁₀ H₈	40.32	0.192
Butylbenzene	C₁₀ H₁₄	44.07	0.2378
Isobutylbenzene	C₁₀ H₁₄	40.4	0.2215
o-Cymene	C₁₀ H₁₄	42.7	0.234
p-Cymene	C₁₀ H₁₄	45.27	0.2478
p-Diethylbenzene	C₁₀ H₁₄	45.03	0.2439
1,2,4,5-Tetramethylbenzene	C₁₀ H₁₄	45.8	0.24
Decane	C₁₀ H₂₂	52.88	0.3051
1-Decanol	C₁₀ H₂₂ O	57.45	0.2971
Undecane	C₁₁ H₂₄	60.88	0.3396
Biphenyl	C₁₂ H₁₀	47.16	0.213
Dodecane	C₁₂ H₂₆	69.14	0.3741
1-Dodecanol	C₁₂ H₂₆ O	72.69	0.3598
Diphenylmethane	C₁₃ H₁₂	60.46	0.2798
Tridecane	C₁₃ H₂₈	77.94	0.4109
1-Tridecanol	C₁₃ H₂₈ O	81.2	0.3942
1-Tetradecanol	C₁₄ H₃₀ O	89.91	0.4289
Pentadecane	C₁₅ H₃₂	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