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A gas mixture consists of 2 moles of O₂ and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is

Asked in NEET 2017 · Internal energy of a gas

Answer: (3) 11 RT

Step-by-step solution

Idea: for n moles with f degrees of freedom, U=(n f)/2RT.

Oxygen is diatomic and vibrations are to be ignored, so f=5.

U_O₂=2×5/2RT=5RT.

Argon is monatomic, so f=3.

U_Ar=4×3/2RT=6RT.

U=5RT+6RT=11 RT.

Why the other options are wrong

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