In a real gas, as the internal energy depends on temperature and volume, the derived equation for an ideal gas (dQ)p​=(dQ)v​+nR dT will change to (dQ)p​=(dQ)v​+nR dT+k , where k is the change in internal energy (positive) due to change in volume when pressure is kept constant. So, in the case of a real gas, for n=1 mole (say),Cp​−Cv​=R+ dTk​ ⇒Cp​−Cv​>R where Cp​ and Cv​ are the specific heat capacities at constant pressure and volume, respectively.