Consider two ideal diatomic gases A and B at some temperature T. Molecules of the gas A are rigid, and have a mass m. Molecular of the gas B has an additional vibrational mode,  and  have a mass m4 . The  ratio of the specific heats (CVA   and  CVB ) of gas A and B ,  respectively is :

For Gas A (diatomic),  degree of freedom (f) = 3+2 = 5  For Gas B (diatomic + vibration),  degree of freedom (f) = 3+2 +2= 7In general, for any gas Specific heat at constant volume CV=fR2Specific heat at constant volume of   A=52RTSpecific heat at constant volume of    B=72RT             ∴  Ratio=57