First slide
Change in internal energy
Question

6 moles of oxygen, 4 moles of Ar. and 2 moles of water vapour form an ideal gas mixture. The mixture is made to expand adiabatically from an initial temperature 127°C to a final temperature 27°C, decrease of internal energy of the mixture is: (take R=2 cal/mol-K)

Moderate
Solution

Decrease in internal energy =-∆U
=(n1CV1+n2CV2+n3CV3)(T1-T2) =6×52R+4×32R+2×3R100=2700 R=5400 cal

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