Name: gas temperature changes in adiabatic processes
Uploaded: 2023-04-30T12:32:28.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Physical Science

HS. Energy

HS-PS3-3.

Adiabatic Processes for an Ideal Gas

Un proceso termodinámico sin transferencia de calor dentro o fuera del sistema se denomina adiabático.
Así, según la primera ley de la termodinámica, el cambio en la energía interna es el negativo del trabajo realizado en un proceso adiabático.
Por ejemplo, un pistón de incendio que consta de un tubo aislado térmicamente tiene un extremo cerrado y el otro extremo tiene un émbolo móvil. 
Si se coloca un pequeño trozo de bola de algodón dentro del tubo y se permite que el émbolo empuje rápidamente hacia abajo a temperatura ambiente, la bola de algodón se incendia a pesar de que no se aplica calor. Esto sucede debido a la compresión adiabática.
Aquí, a medida que el volumen disminuye, el trabajo realizado se vuelve negativo; por lo tanto, el cambio de energía interna es positivo, con un aumento correspondiente en la temperatura del gas.
Por el contrario, al abrir una botella de bebida carbonatada enfriada, el gas atrapado en la botella sufre una expansión adiabática, lo que hace que el trabajo realizado sea positivo.
Como resultado, la energía interna disminuye con una caída de temperatura correspondiente, condensando el vapor evaporado en una nube visible.

<ol>
	<li>Young, H.D. y Freedman, R.A. (2012). Física Universitaria con Física Moderna. San Francisco, CA: Pearson. Pág. 640.</li>
	<li>OpenStax. (2019). Física Universitaria Vol. 2. [Versión web]. Obtenido de <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>

procesos adiabáticos para un gas ideal

Cuando un gas ideal es comprimido adiabáticamente, es decir, sin añadir calor, se realiza trabajo sobre él y su temperatura aumenta. En una expansión adiabática, el gas realiza trabajo y su temperatura disminuye. Las compresiones adiabáticas ocurren en realidad en los cilindros de un automóvil, donde las compresiones de la mezcla de gas-aire suceden tan rápidamente que no hay tiempo para que la mezcla intercambie calor con su entorno. Sin embargo, debido a que se realiza trabajo sobre la mezcla durante la compresión, su temperatura se incrementa significativamente. De hecho, el aumento de temperatura puede ser tan grande que la mezcla puede explotar sin la adición de una chispa. Estas explosiones, al no estar sincronizadas, hacen que el automóvil funcione mal, generalmente hace "ruido". A medida que la temperatura de ignición aumenta con la octanaje de la gasolina, el uso de gasolina de mayor octanaje es una forma de superar este problema. Otro proceso adiabático interesante es la expansión libre de un gas. Imagina que un gas está confinado por una membrana en un lado de un recipiente de dos compartimentos y aislado térmicamente. Cuando la membrana se perfora, el gas se precipita hacia el lado vacío del recipiente, expandiéndose libremente. Como el gas se expande "hacia un vacío", la presión disminuye (p = 0), no realiza trabajo y, debido al aislamiento térmico del recipiente, la expansión es adiabática. Con Q = 0 y W = 0 en la primera ley, dU = 0, por lo que la energía interna en los estados de equilibrio inicial y final es la misma para la expansión libre. Si el gas es ideal, la energía interna depende solo de la temperatura. Por lo tanto, cuando un gas ideal se expande libremente, su temperatura no cambia.

Procesos adiabáticos para un gas ideal

Cuando un gas ideal se comprime adiabáticamente, es decir, sin añadir calor, se trabaja sobre él y su temperatura aumenta. En una expansión adiabática, ...

Education

Educación

JoVE Core

Physics

Física

Unit 1

Unidad 1

The First Law of Thermodynamics

La primera ley de la termodinámica

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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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adiabatic processes for an ideal gas

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...

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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.

Gas Temperature Changes in Adiabatic Processes | JoVE K12

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Gas Temperature Changes in Adiabatic Processes

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