A diatomic ideal gas is heated at constant volume until the pressure is doubled and again heated at constant pressure until the volume is doubled. The average molar heat capacity for the whole process is

Let initial pressure, volume and temperature be P0,V0 and T0, respectively, indicated by state A in P-V diagram. The gas is then isochorically taken to state B 2P0,V0,2T0 and then taken from state B to state C2P0,2V0,4T0 isobarically.Total heat absorbed by 1 mol of gasQ=Cv2T0−T0+CP4T0−2T0=52RT0+72R×2T0=192RT0Total change in temperature from series A to C is ΔT=3T0Therefore,    Molar heat capacity =QΔT=192RT03T0=196R