Can heat capacity at constant volume for a gas decrease as temperature increases? 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?
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: