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-

• A. $\frac{5}{2}RT$
• B. $\frac{3}{2}RT$
• C. $\frac{9}{2}RT$
• D. $3RT$

Answer 1

The correct option is D $3RT$

For triatomic non-linear molecule, the degree of freedom, $f=3+3=6$

Internal energy of a mole of the gas at temperature $T$ is,

$U=\frac{f}{2}nRT=\frac{6}{2}RT=3RT$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(D\right)$ is the correct answer.