Question
Given below are observations on molar specific heats at room temperature of some common gases.
| Gas | Molar specific heat(CV) |
| Hydrogen | 4.87 |
| Nitrogen | 4.97 |
| Oxygen | 5.02 |
| Nitric Oxide | 4.99 |
| Carbon Monoxide | 5.01 |
| Chlorine | 6.17 |
The measured molar specific heats of these gases are markedly different from those for monatomic gases. Typically, molar specific heat of a monatomic gas is 2.92 cal/mol K. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine?
Solution
The above-listed gases are diatomic. Diatomic gases have other degree of freedom apart from the translational degree of freedom.
Inorder to increase the temperature of these gases, heat must be supplied to them. this heat increases the average energy of all the modes of motion. Hence, the molar specific heat of diatomic gases is more than that of monatomic gases.
For only rotational motion,
Molar specific heat of the diatomic gas is = (5/2) R
= 
Apart from Chlorine in the above list, for all gases molar specific heat is (5/2) R.
At room temperature, Chlorine has vibrational modes apart from rotational and translational modes of motion.
