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Thermal Properties Of Matter

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

4 RT

15 RT

9 RT

11 RT

Solution

11 RT

straight U space equals space straight n subscript 1 straight f subscript 1 over 2 RT space plus space straight n subscript 2 straight f subscript 2 over 2 RT equals space 2 space straight x space 5 over 2 space RT space plus space 4 space straight x space 3 over 2 space RT space equals space 5 RT space plus space 6 RT straight U space equals space 11 space RT