page_title: Adiabatic process
section_title: Ideal gas (reversible process)
hierarchical_section_title: Adiabatic process / Ideal gas (reversible process)
context_page_description: An adiabatic process occurs without transferring heat or mass between a thermodynamic system and its surroundings. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work. It also conceptually undergirds the theory used to expound the first law of thermodynamics and is therefore a key thermodynamic concept.
  Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation". For example, the adiabatic flame temperature uses this approximation to calculate the upper limit of flame temperature by assuming combustion loses no heat to its surroundings.
  In meteorology and oceanography, adiabatic cooling produces condensation of moisture or salinity, oversaturating the parcel. Therefore, the excess must be removed. There, the process becomes a pseudo-adiabatic process whereby the liquid water or salt that condenses is assumed to be removed upon formation by idealized instantaneous precipitation. The pseudoadiabatic process is only defined for expansion because a compressed parcel becomes warmer and remains undersaturated.
context_section_description: The mathematical equation for an ideal gas undergoing a reversible (i.e., no entropy generation) adiabatic process can be represented by the polytropic process equation
  where P is pressure, V is volume, and for this case n = γ, where
  CP being the specific heat for constant pressure, CV being the specific heat for constant volume, γ is the adiabatic index, and f 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, γ = , and for a diatomic gas (such as nitrogen and oxygen, the main components of air) γ = . 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 that
  where T is an absolute temperature. This can also be written as
caption: For a simple substance, during an adiabatic process in which the volume increases, the internal energy of the working substance must decrease