The equation of state of a certain gas is (k is constant)
v=RTP+kRT
Then the value of k for the process of throttling of gas from initial pressure P1 and temperature T1 to final pressure P2 and tempertaure T2 is
dh=cpdT+[v−T(δvδT)p]dp
during throttling dh = 0 and the above equations gives
cpdT=−[v−T(δvδT)p]dv
Noe from the given equation of state
(δvδT)p=RP−kRT2
Substituting thus in the above equation,
cpdT=−[RTP+kRT−kRT]dp
=−2kRTdp
on rearanging
Tdtk=−2cPRcp
T22−T212k=−2(P2−P1)RCp
T22−T214k=P1−P2)RCp
k=(T22−T214(P1−P2))Rcp