Finally, heat content of the CO2 will be higher because of the higher specific
heat at constant volume because there are 3 modes of vibrational motion rather than one (N2).
There's an intense and cautious feeling to Sakamoto and Nicolai's approach, keeping
everything at a constant volume and introducing changes only gradually.
Physicists like to do thermodynamic
calculations at constant volume as the equations are simpler, or that's what I remember Feynman saying in freshman physics.
Cp is the heat capacity at constant pressure, Cv is the heat capacity
at constant volume.