Q.

Figure below shows two paths that may be taken by a gas to go from a state A to a state C. In process AB, 400 J of heat is added to the system and in process BC, 100 J of heat is added to the system. The heat absorbed by the system in the process AC will be         [2015]

1 460 J  
2 300 J  
3 380 J  
4 500 J  

Ans.

(1)

As initial and final points for two paths are same so

ΔUABC=ΔUAC

AB is isochoric process.

         ΔWAB=0

QAB=ΔUAB=400 J

BC is isobaric process.

ΔQBC=ΔUBC+ΔWBC

100=ΔUBC+6×104(4×10-3-2×10-3)

100=ΔUBC+12×10

ΔUBC=100-120=-20J

As, ΔUABC=ΔUAC,  ΔUAB+ΔUBC=ΔQAC-ΔWAC

400-20=ΔQAC-(2×104×2×10-3+12×2×10-3×4×104)

ΔQAC=460J