Q.

One mole of an ideal diatomic gas undergoes a transition from A to B along a path AB as shown in the figure. The change in internal energy of the gas during the transition is   [2015]

1 20 J  
2 - 12 kJ  
3 20 kJ  
4 - 20 kJ  

Ans.

(4)

We know, ΔU=nCVΔT

=n(5R2)(TB-TA)             [For diatomic gas, CV=5R2]

=5nR2(PBVBnR-PAVAnR)               [PV=nRT]

=52(PBVB-PAVA)=52(2×103×6-5×103×4)

=52(-8×103)=-20 kJ