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)25RT
(B)23RT
(C)3 RT✓ Correct
(D)29RT
Answer: (C)
Solution
A rigid triangular (non-linear) triatomic molecule has three translational and three rotational degrees of freedom, so f=6. By equipartition the internal energy of one mole is U=2fRT=26RT=3RT.
JEE Main · 2020 · 03 Sep 2020 · Shift 1 · Single correct option