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At ordinary temperatures, molecules of a diatomic gas possess only translational and rotational kinetic energies. At high temperatures, vibrational energy modes also become active. Compared to lower temperatures, a diatomic gas at higher temperature will have —

1. lower molar heat capacity.
2. higher molar heat capacity.
3. lower isothermal compressibility.
4. higher isothermal compressibility.

Correct answer: higher molar heat capacity.

Solution

At high temperatures vibrational modes (each contributing R to Cv) become active, increasing the molar heat capacity. Isothermal compressibility of an ideal gas is 1/P, independent of temperature or degrees of freedom.

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