Adiabatisch

Adiabatic is a term used in physics and chemistry to describe a process or system in which no heat is exchanged with the surroundings. In thermodynamics, this means the heat transfer Q between the system and its environment is zero. As a consequence, changes in the system’s internal energy U arise solely from work performed by or on the system, according to the first law of thermodynamics (dU = -dW when Q = 0).

For a simple compressible system, an ideal gas undergoing a reversible adiabatic process satisfies PV^gamma = constant, where gamma is the heat capacity ratio Cp/Cv. Equivalently, T V^(gamma-1) = constant and P^(1-γ) T^γ = constant. These relations show how pressure, volume, and temperature evolve together during an adiabatic change: expansion cools the gas, while compression heats it. Because no heat is exchanged, adiabatic processes generally exhibit larger temperature changes than comparable isothermal processes.

In practice, adiabatic conditions occur during rapid processes or when a system is well insulated from its surroundings. They are important in engineering applications such as piston engines, turbines, and compressors, as well as in atmospheric science, where they underpin concepts like the dry adiabatic lapse rate (about 9.8°C per kilometer) and the behavior of rising air parcels. Real-world adiabatic processes may be close to ideal if heat transfer is minimized, though real systems can deviate due to irreversibilities and phase changes.

In quantum mechanics, the adiabatic theorem states that a system evolving slowly relative to its energy gaps tends to stay in its instantaneous eigenstate, underpinning methods like the Born–Oppenheimer approximation and various slow-change analyses.