Vander Waal's Equation
To rectify the errors caused by ignoring the intermolecular forces of attraction and the volume occupied by molecules, Vander Waal (in 1873) modified the ideal gas equation by introducing two corrections,
(i) Volume correction
(ii) Pressure correction
Vander Waal's equation is obeyed by the real gases over wide range of temperatures and pressures, hence it is called equation of state for the real gases.