Question
Question: In changing the state of a gas adiabatically from an equilibrium state A to another equilibrium stat...
In changing the state of a gas adiabatically from an equilibrium state A to another equilibrium state B an amount of work equal to 22.3 J is done on the system. If the gas is taken from state A to B via a process in which the net heat absorbed by the system is 9.35 cal then the net work done by the system in latter case is (Take 1 cal = 4.2 J)
A
15 J
B
16 J
C
17 J
D
18 J
Answer
17 J
Explanation
Solution
: In the first case,
For adiabatic change ΔQ=0
The work is done on the system is
ΔW=−22.3J
According to first law of thermodynamics
}{0 = \Delta U - 22.3 }{\Delta U = 22.3J}$$ In the second case $${\Delta Q = 9.35cal = 9.35 \times 4.2J = 393.3J }{As\Delta Q = \Delta U + \Delta W }{\therefore\Delta W = \Delta Q - \Delta U }{\therefore\Delta W = 39.3 - 22.3 = 17J}$$ ($\therefore\Delta U$will be same be for both the cases)