Some van der Waals Constants Substance a (J. m3/mole2) b (m3/mole) Pc (MPa) Tc (K)  Air .1358 3.64×10–5 3.77 133  Carbon Dioxide (CO2) .3643 4.27×10–5 7.39 304.2  Nitrogen (N2) .1361 3.85×10–5 3.39 126.2  Hydrogen (H2) .0247 2.65×10–5 1.30 33.2  Water (H2O) .5507 3.04×10–5 22.09 647.3  Ammonia (NH3) .4233 3.73×10–5 11.28 406  Helium (He) .00341 2.34×10–5 0.23 5.2  Freon (CCl2F2) 1.078 9.98×10–5 4.12 385   gas    H2 0.024 76 0.026 61  He 0.003 456 0.023 70  CO2 0.363 9 0.042 67  H2O 0.553 5 0.030 49  O2 0.137 8 0.031 83  N2 0.140 8 0.039 13   Gas Formula a [(L2 · atm)/mole2] b [L/mole]  Helium He 0.03412 0.02370  Hydrogen H2 0.2444 0.02661  Nitrogen N2 1.390 0.03913  Oxygen O2 1.360 0.03183  Carbon dioxide CO2 3.592 0.04267  Acetylene C2H2 4.390 0.05136  Chlorine Cl2 6.493 0.05622  n - Butane C4H10 14.47 0.1226  n - Octane C8H18 37.32 0.2368   Element Atomic Radius Molecular Volume van der Waals a constant* van der Waals b constant*  Hydrogen 0.79 3.3 0.24 0.027  Helium 0.49 0.49 0.03 0.024  Neon 0.51 0.55 0.21 0.017