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

Um processo termodinâmico sem transferência de calor dentro ou fora do sistema é denominado adiabático.
Assim, de acordo com a primeira lei da termodinâmica, a mudança na energia interna é o negativo do trabalho realizado em um processo adiabático.
Por exemplo, um pistão de fogo que consiste em um tubo isolado termicamente tem uma extremidade fechada e a outra extremidade tem um êmbolo móvel. 
Se um pequeno pedaço de bola de algodão for colocado dentro do tubo e o êmbolo for empurrado para baixo rapidamente à temperatura ambiente, a bola de algodão pega fogo apesar de nenhum calor ser aplicado. Isso acontece devido à compressão adiabática.
Aqui, à medida que o volume diminui, o trabalho realizado torna-se negativo; portanto, a mudança de energia interna é positiva, com um aumento correspondente na temperatura do gás.
Por outro lado, ao abrir uma garrafa de bebida carbonatada resfriada, o gás preso na garrafa sofre expansão adiabática, resultando em um trabalho realizado.
Como resultado, a energia interna diminui com uma queda de temperatura correspondente, condensando o vapor evaporado em uma nuvem visível.

<ol>
	<li>Young, H.D. e Freedman, R.A. (2012). Física Universitária com Física Moderna. São Francisco, CA: Pearson. PÁG. 640.</li>
	<li>OpenStax. (2019). Física Universitária Vol. 2. [Versão Web]. Obtido 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>

processos adiabáticos para um gás ideal

Quando um gás ideal é comprimido adiabaticamente, ou seja, sem adição de calor, trabalho é realizado sobre ele e sua temperatura aumenta. Em uma expansão adiabática, o gás realiza trabalho e sua temperatura diminui. Compressões adiabáticas ocorrem nos cilindros de um carro, onde as compressões da mistura de gasolina e ar ocorrem tão rapidamente que não há tempo para a mistura trocar calor com o ambiente. No entanto, como trabalho é realizado na mistura durante a compressão, sua temperatura aumenta significativamente. De fato, o aumento de temperatura pode ser tão grande que a mistura pode explodir sem a adição de uma faísca. Tais explosões, como não são controladas, fazem o carro funcionar mal. Como a temperatura de ignição aumenta com a octanagem da gasolina, o uso de gasolina de octanagem mais alta é uma forma de resolver esse problema.

Outro processo adiabático interessante é a expansão livre de um gás. Imagine que um gás esteja confinado por uma membrana em um lado de um recipiente de dois compartimentos e termicamente isolado. Quando a membrana é perfurada, o gás se precipita para o lado vazio do recipiente, expandindo-se livremente. À medida que o gás se expande "contra um vácuo", a pressão diminui (p = 0), ele não realiza trabalho e, como o recipiente é termicamente isolado, a expansão é adiabática. Com Q = 0 e W = 0, da primeira lei, dU = 0 e, portanto, a energia interna nos estados de equilíbrio inicial e final é a mesma para a expansão livre. Se o gás for ideal, a energia interna depende apenas da temperatura. Portanto, quando um gás ideal se expande livremente, sua temperatura não muda.

Processos Adiabáticos para um Gás Ideal

Quando um gás ideal é comprimido adiabaticamente, ou seja, sem adição de calor, o trabalho é feito sobre ele e sua temperatura aumenta. Em uma expansão adiabática, ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

The First Law of Thermodynamics

A Primeira Lei da Termodinâmica

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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...

pressure and volume in an adiabatic process

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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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