ISENTROPIC PROCESS
When the entropy in a gas that has been compressed or expanded is constant, no heat exchange with the surroundings takes place. This change in state follows Poison's law.
P2/P1 = (V1/V2)k  => P2/P1  =  (T2/T1)k/k-1
  P : absolute pressure ( Pa )
  V : volume (m3)
  T : absolute temperature ( K )
  k = Cp/Cv