Name: gas temperature changes in adiabatic processes
Uploaded: 2023-04-30T12:32:28.000Z
Duration: 1 min 18 s
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Adiabatic Processes for an Ideal Gas

Ein thermodynamischer Prozess ohne Wärmeübertragung innerhalb oder außerhalb des Systems wird als adiabatisch bezeichnet.
Nach dem ersten Hauptsatz der Thermodynamik ist die Änderung der inneren Energie also das Negativ der Arbeit, die in einem adiabatischen Prozess geleistet wird.
Zum Beispiel hat ein Feuerkolben, der aus einem wärmeisolierten Rohr besteht, ein geschlossenes Ende und das andere Ende einen beweglichen Kolben. 
Wenn ein kleines Stück Wattebausch in das Rohr gesteckt wird und der Kolben bei Raumtemperatur schnell nach unten gedrückt wird, fängt der Wattebausch Feuer, obwohl keine Hitze angewendet wird. Dies geschieht aufgrund der adiabatischen Kompression.
Hier wird die geleistete Arbeit mit abnehmendem Volumen negativ, d.h. die innere Energieänderung ist positiv, mit einem entsprechenden Anstieg der Gastemperatur.
Umgekehrt erfährt beim Öffnen einer Flasche mit gekühltem kohlensäurehaltigem Getränk das in der Flasche eingeschlossene Gas eine adiabatische Expansion, was dazu führt, dass die geleistete Arbeit positiv ist.
Infolgedessen nimmt die innere Energie mit einem entsprechenden Temperaturabfall ab, wodurch der verdampfte Dampf zu einer sichtbaren Wolke kondensiert.

<ol>
	<li>Young, H.D. und Freedman, R.A. (2012). Universitätsphysik mit moderner Physik. San Francisco, Kalifornien: Pearson. S. 640.</li>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/books/university-physics-volume-2/pages/3-6-adiabatic-processes-for-an-ideal-gas">https://openstax.org/books/university-physics-volume-2/pages/3-6-adiabatic-processes-for-an-ideal-gas</a></li>
</ol>

adiabatische prozesse für ein ideales gas

Wenn ein ideales Gas adiabatisch, d. h. ohne Zufuhr von Wärme, komprimiert wird, wird Arbeit verrichtet und seine Temperatur steigt. Bei einer adiabatischen Expansion verrichtet das Gas Arbeit und seine Temperatur fällt. Adiabatische Berdichtungen kommen in der Tat in den Zylindern eines Autos vor, wo die Kompressionen der Gas-Luft-Mischung so schnell stattfinden, dass keine Zeit für den Wärmeaustausch mit der Umgebung bleibt. Trotzdem steigt die Temperatur der Mischung aufgrund der Kompression signifikant an. Tatsächlich kann die Temperaturerhöhung so groß sein, dass die Mischung ohne das Hinzufügen eines Funken explodieren kann. Da solche Explosionen nicht zeitlich abgestimmt sind, läuft ein Auto in der Regel schlecht - es "klopft" normalerweise. Da die Zündtemperatur mit der Oktanzahl des Benzins steigt, ist die Verwendung von höheroktanigem Benzin eine Möglichkeit, dieses Problem zu bewältigen.

Ein weiterer interessanter adiabatischer Prozess ist die freie Expansion eines Gases. Stellen Sie sich vor, ein Gas ist durch eine Membran auf einer Seite eines zweikammerigen, thermisch isolierten Behälters eingeschlossen. Wenn die Membran durchstochen wird, strömt das Gas in die leere Seite des Behälters und dehnt sich somit frei aus. Da das Gas sich "gegen ein Vakuum" ausdehnt, nimmt der Druck ab (p = 0), es verrichtet keine Arbeit und die Expansion ist aufgrund der thermischen Isolierung adiabatisch. Mit Q = 0 und W = 0 im ersten Hauptsatz der Thermodynamik, ist dU = 0; daher ist die innere Energie im Anfangs- und Endgleichgewichtszustand für die freie Expansion gleich. Wenn das Gas ideal ist, hängt die innere Energie nur von der Temperatur ab. Daher ändert sich die Temperatur eines idealen Gases bei freier Expansion nicht.

Adiabatische Prozesse für ein ideales Gas

Wenn ein ideales Gas adiabatisch komprimiert wird, dh ohne Wärmezufügung, wird daran gearbeitet und seine Temperatur steigt. Bei einer adiabatischen Expansion ...

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gas temperature changes in adiabatic processes

Adiabatic processes change the temperature of an ideal gas without heat transfer. In an adiabatic compression, no heat is added, but work is done on the gas. That work raises the gas temperature. In an adiabatic expansion, the gas does work and its temperature drops.

A common example is the compression of a gas-air mixture inside a car engine cylinder. The compression happens so quickly that there is no time for heat to move between the mixture and its surroundings. Even so, the work done on the mixture can raise its temperature enough for it to explode without a spark. When that explosion happens at the wrong time, the engine knocks and runs poorly. Higher-octane gasoline can help because it has a higher ignition temperature.

The transcript also describes free expansion of a gas. In this case, a gas starts on one side of a thermally insulated two-compartment container. When the membrane is punctured, the gas rushes into the empty side and expands into a vacuum. Because the pressure outside is zero, the gas does no work. Since the container is thermally insulated, the process is adiabatic. With Q = 0 and W = 0, the first law gives dU = 0, so the internal energy stays the same before and after the expansion. For an ideal gas, internal energy depends only on temperature, so the temperature does not change during free expansion.

Gas Temperature Changes in Adiabatic Processes

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Learn how adiabatic compression and free expansion affect an ideal gas. See why temperature rises in compression, drops in expansion, and stays the same in free expansion.

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Gas Temperature Changes in Adiabatic Processes

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