Ideal Gas Vs Real gas
For real gases there are some contradictions in the assumptions made while defining real gases. 
Therefore some corrections were needed in the equation which were given by van der waals in his real gas equation 
The van der Waals equation corrects for the volume of, and attractive forces between, gas molecules:

(P+a(n/v)^2)(V-nb) = nRT

There are two corrective factors in van der Waals equation. The first,   , alters the pressure in the ideal gas equation. It accounts for the intermolecular attractive forces between gas molecules. The magnitude of a is indicative of the strength of the intermolecular attractive force.

The factor - nb accounts for the volume occupied by the gas molecules. b has units of L/mol. Since b corresponds to the total volume per mole occupied by gas molecules, it closely corresponds to the volume per mole of the liquid state, whose molecules are closely layered. b is generally much smaller in magnitude than a . The values of a and b generally increase with the size and complexity of the molecule.