5.6 litre of helium gas at STP is adiabatically compressed to 0.7 litre. Taking the initial temperature to be T1, the work done on the gas is:
For an adiabatic process, TVγ−1=constant
or T1Vγ−11=T2Vγ−12
where V1=5.6 L and V2=0.7 L
also, He is monoatomic so γ=53
so, T1(5.6)23=T2(0.7)23
this gives T2=4T1
V1=5.6 L at STP so, moles of gas n=5.622.4=14
work done by the gas in adiabatic process is given by,
w=P2V2−P1V1γ−1
=nRT2−nRT1γ−1
=nRΔTγ−1
Substituting these values to get
w=R(4T1−T1)4×2/3
w=98RT1