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.

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.