Question

According to law of equipartition of energy the molar specific heat of a non rigid diatomic gas at constant volume is

• A. \((9/2)R\)
• B. \((5/2)R\)
• C. \((3/2)R\)
• D. \((7/2)R\)

Hint:

A non-rigid diatomic molecule has 7 degrees of freedom, so \(C_V=\frac72R\).

Answer 1

The Correct Option is D

Step 1: Idea:
Add one vibrational mode to the rigid rotator result.

Step 2: Steps:
A rigid diatomic gas has $C_V = \frac52R$. A vibrational mode adds $R$ (two quadratic terms, $\frac12R$ each). So $C_V = \frac52R + R = \frac72R$.

Final Answer:
$C_V = \frac72R$, option (D). \[ \boxed{\frac{7}{2}R} \]