Question:
Consider a gas of triatomic molecules. The molecules are assumed to be triangular and made of massless rigid rods whose vertices are occupied by atoms. The internal energy of a mole of the gas at temperature T is :
Consider a gas of triatomic molecules. The molecules are assumed to be triangular and made of massless rigid rods whose vertices are occupied by atoms. The internal energy of a mole of the gas at temperature T is :
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A rigid non-linear triatomic molecule has 3 translational and 3 rotational degrees of freedom, and no vibrational ones.
Updated On: Nov 5, 2026
- \(\frac{3}{2}RT\)
- \(\frac{9}{2}RT\)
- \(\frac{5}{2}RT\)
- \(3RT\)
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The Correct Option is D
Solution and Explanation
The molecule is rigid (massless rigid rods), so there are no vibrational modes.
It is non-linear (triangle): 3 translational + 3 rotational = 6 degrees of freedom.
By equipartition each degree of freedom contributes \(\frac12 RT\) per mole.
\(U = 6 \times \frac12 RT = 3RT\).
Answer: (4) \(3RT\)
It is non-linear (triangle): 3 translational + 3 rotational = 6 degrees of freedom.
By equipartition each degree of freedom contributes \(\frac12 RT\) per mole.
\(U = 6 \times \frac12 RT = 3RT\).
Answer: (4) \(3RT\)
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