van der Waals Constants

Substance

a

(J. m3/mole2)

b

(m3/mole)

Pc

(MPa)

Tc

(K)

Air

1.1358

3.64x10-5

3.77

133

Carbon Dioxide (CO2)

1.3643

4.27x10-5

7.39

304.2 

Nitrogen (N2)

1.1361

3.85x10-5

3.39

126.2 

Hydrogen (H2)

1.0247

2.65x10-5

1.30

33.2 

Water (H2O)

1.5507

3.04x10-5

22.09

647.3 

Ammonia (NH3)

1.4233

3.73x10-5

11.28

406 

Helium (He)

1.00341

2.34x10-5

0.23

5.2 

Freon (CCl2F2)

1.0780

9.98x10-5

4.12

385 


Observe that inert gases like Helium have a low value of a as one would expect since such gases do not interact very strongly, and that large molecules like Freon have large values of b.