Q: A perfect gas goes from state A to another state B by absorbing 8 × 105 J of heat and doing 6.5 × 105 J of external work. It is now transferred between the same two states in another process in which it absorbs 105 J of heat. Then in the second process
(a) Work done on the gas is 0.5 × 105 J
(b) Work done by gas is 0.5 × 105 J
(c) Work done on gas is 105 J
(d) Work done by gas is 105 J
Ans: (a)
Sol: In Process First:
Applying First Law of Thermodynamics ,
∆Q = ∆U + ∆W
8 × 105 = ∆U + 6.5 × 105
∆U = 1.5 × 105 J
In Process Second :
Applying First Law of Thermodynamics ,
∆Q = ∆U + ∆W
10^5 = 1.5 × ∆W
⇒ ∆W = – 0.5 × 105 j