Two moles of helium gas `(r=5//3)` are initially at a temperature of `27^(@)C` and occupy a volume of `20` litre. The gas is first expanded at constant pressure until the volume is doubled. It then undergoes adiabatic change until the temperature returns to its intial value.
(a) Sketch the process on `P-V` diagram.
(b) What are final pressure and final volume of gas?
(c) What is the work done by the gas?

Options

A. `2.46` atm, `110L`
B. `4.9` atm, `113.13L`
C. `2.46` atm, `13.13L`
D. `4.9` atm `110L`

Answer

C, D

Explanation

For state `A P_(1)=(nRT)/V=2.46` atm
For isobaric process `AB (V_(1))/(T_(1))=(V_(2))/(T_(2))`
`T_(2)=600K`
For adiabatic process `BC TV^(lamda-1)=` constant
`600(40)^(gamma-1)=300(V_(1))^(gamma-1)`
`V_(1)=113.13` lit