Kinetic molecular theory makes convinced assumptions about gases that are, in fact, not true for real gases. Consequently the measured properties of a gas are often slightly different from the values predicted by the ideal gas law. The van der Waals equation is a more exact way of computing properties of real gases. The formula comprise two constants, a and b, that are unique for each gas.

The van der Waals equation is ,( P+ an2/v2) (V-nb) = nRT
Where P is the pressure, n the number of moles of gas, V the volume, T the temperature, R and the gas constant.

All real gases possess intermolecular forces that can slightly reduce the observed pressure. In the van der Waals equation, the variable P is adjusted to, where a is the attractive force between molecules. (P+ an2/v2)

The volume of a gas is described as the space in which the gas molecules can move. When utilizing the ideal gas law we make the assumption that this space is equal to the volume of the container. But, the gas molecules themselves take up few spaces in the container. Thus in the van der Waals equation, the variable V is adjusted to be the volume of the container minus the space taken up by the molecules, V-nb, where b is the volume of a mole of molecules.

14.0 moles of gas are in a 5.00L tank at 23.7C. Compute the difference in pressure between methane as well as an ideal gas under these conditions. The van der Waals constants for methane are a=1.345 (L2*atm)/mol2 and b =0.03219L/mol.