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Question:

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?

15 RT

4 RT

9 RT

11 RT

Solution:

Total internal energy
ν = fO2/2 * nO2 * RT + fAr/2 * nAr
ν = 5/2 * 2RT + 3/2 * 4RT
ν = 5RT + 6RT
ν = 11RT