I found a function for the $C_V$ of a gas which is being heated under constant volume,but the function shows that the $C_V$ is decreasing. I was wondering if this is possible for any gas since I know the $C_V$ is supposed to increase with temperature. Is there any reason why this would happen?
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$\begingroup$ Handbook of Chemistry and Physics, Chemical Engineers' Handbook, NIST, Fundamentals of Engineering Thermodynamics (Moran et al) $\endgroup$ – Chet Miller Mar 29 '18 at 15:41
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As temperature increases, it activates the rotational and vibrational degrees of freedom, so $\ce{Cv}$ increases with increase in temperature. The graph $\ce{CO2}$ would be:
