The mathematical equation for an ideal gas undergoing a reversible (i.e., no entropy generation) adiabatic process iswhere P is pressure, V is volume, and being the specific heat for constant pressure,  being the specific heat for constant volume,  is the adiabatic index, and  is the number of degrees of freedom (3 for monatomic gas, 5 for diatomic gas and collinear molecules e.g. carbon dioxide).For a monatomic ideal gas, , and for a diatomic gas (such as nitrogen andoxygen, the main components of air) .[10] Note that the above formula is only applicable to classical ideal gases and not Bose–Einstein or Fermi gases.For reversible adiabatic processes, it is also true thatwhere T is an absolute temperature.This can also be written as
1 5 1