The ideal gas law is one example of an equation of state. It relates the pressure, volume, temperature and amount of gas. Another equation of state which better models real gases is the van der Waals equation: [P+a (n/V)2] (V – nb) =nRT. In the van der Waals equation, a and b are constants which depend on what type of gas you have. The constant “a” is determined with the strength of intermolecular forces and is quite large for water vapor compared to the noble gases. The constant “b” is decided with the size of the molecules. Larger molecules have larger values for “b”.
a) What are the SI units for “a” and “b”?
b) Solve the van der Waals equation for P.
c) Decide the work done with n moles of a van der Waals gas which expands isothermally at a temperature T from a volume V1 to a volumeV2.