Name: isothermal expansion and heat transfer
Uploaded: 2025-08-19T15:10:28.000Z
Duration: 1 min 21 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Chemistry

Energy

HS-PS3-4

Isothermal Processes

Um processo termodinâmico que ocorre a uma temperatura constante é chamado de processo isotérmico.
A conversão de água fervente em vapor a uma temperatura constante de 100 graus Celsius é um exemplo de processo isotérmico. Da mesma forma, a conversão de água em gelo a 0 graus Celsius também é um processo isotérmico.
A mudança na energia interna é zero para esses processos, pois a temperatura não muda. Assim, usando a primeira lei da termodinâmica, o trabalho realizado é igual ao calor.
Agora, considere um sistema de gás ideal fechado em uma seringa de gás selada a uma temperatura constante.
Quando o êmbolo é empurrado lentamente de maneira controlada, o gás dentro da seringa é comprimido. O volume reduzido do gás provoca um aumento da pressão, porém a temperatura permanece constante.
A liberação do êmbolo de maneira controlada leva a uma expansão do gás a temperatura constante.
A curva pV para qualquer processo isotérmico é hiperbólica, uma vez que a pressão é inversamente proporcional ao volume para um gás ideal a uma temperatura constante.

<ol>
	<li>Young, H. D, e Freedman, R.A. (2012). Física Universitária com Física Moderna. São Francisco, CA: Pearson. pág. 635.</li>
	<li>OpenStax. (2019). Física Universitária Vol. 2. [Versão Web]. pp 121 Obtido de <a href="https://openstax.org/books/college-physics/pages/15-2-the-first-law-of-thermodynamics-and-some-simple-processes">https://openstax.org/books/college-physics/pages/15-2-the-first-law-of-thermodynamics-and-some-simple-processes</a></li>
</ol>

processos isotérmicos

Um processo termodinâmico que ocorre a temperatura constante é chamado de processo isotérmico. O calor flui lentamente para dentro ou para fora do sistema para manter o equilíbrio térmico. Processos que envolvem mudanças de fase, como a evaporação da água para o vapor, ou o congelamento da água em gelo a uma temperatura constante, são exemplos de processos isotérmicos.

Um gás ideal também pode passar por expansão ou compressão isotérmica.

Por exemplo, considere 1 mol de um gás ideal dentro de um cilindro isolado com volume inicial V e pressão p. Suponha que o calor adicionado ao sistema cause uma expansão quase-estática do gás a uma temperatura constante de 300 K. Se o volume do gás mudar para 2V, qual é a quantidade de calor adicionada ao sistema?

Aqui, as quantidades conhecidas são o número de moles do gás, o volume inicial e final do gás. A quantidade desconhecida, calor, deve ser calculada.

De acordo com a primeira lei da termodinâmica,

<img alt="Equation1" src="/files/ftp_upload/13682/13682_Equation_PT_1.svg" style="text-align: center; height: 13px;" />

Como a temperatura é constante, a variação de energia interna para este processo é zero. Assim, o calor adicionado ao sistema é igual ao trabalho realizado pelo sistema.

<img alt="Equation2" src="/files/ftp_upload/13682/13682_Equation_PT_2.svg" style="text-align: center; height: 13px;" />

Agora, o trabalho realizado por um gás ideal durante a expansão isotérmica é dado por,

<img alt="Equation3" src="/files/ftp_upload/13682/13682_Equation_PT_3.svg" style="text-align: center; height: 32px;" />

Substituindo o número de moles, a constante do gás, a temperatura, o volume inicial e o volume final do gás, o trabalho realizado é igual a 1728,85 J.

Uma vez que o trabalho realizado pelo sistema é igual ao calor adicionado ao sistema, considera-se que 1728,85 J de calor são aplicados ao sistema para expandi-lo isotermicamente para 2V.

Processos isotérmicos

Um processo termodinâmico que ocorre a temperatura constante é chamado de processo isotérmico. O calor flui lentamente para dentro do sistema ou para fora do sistema para ...

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

isothermal expansion and heat transfer

An isothermal process is a thermodynamic process that happens at constant temperature. During the process, heat slowly flows into the system or out of the system so thermal equilibrium is maintained.

Phase changes are common examples of isothermal processes. Water can evaporate into steam at a constant temperature, and water can also freeze into ice at a constant temperature. An ideal gas can also undergo isothermal expansion or compression.

Here, an ideal gas in an isolated cylinder expands quasistatically at 300 K. The gas starts with 1 mole at volume V and pressure p. The volume then changes to 2V, and the heat added to the system must be found.

By the first law of thermodynamics, the change in internal energy is zero because the temperature stays constant. That means the heat added to the system equals the work done by the system. For an ideal gas in isothermal expansion, the work is calculated from the initial and final volume.

Substituting the number of moles, gas constant, temperature, and volumes gives a work value of 1728.85 J. Since the work done by the gas equals the heat added, 1728.85 J of heat is applied to expand the gas isothermally to 2V.

Isothermal Expansion and Heat Transfer

thermodynamic systems

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isothermal processes

An isothermal process is a thermodynamic process that happens at constant temperature. During the process, heat slowly flows into the system or out of the system so thermal equilibrium is maintained. Phase changes are common examples of isothermal processes. Water can evaporate into steam at a constant temperature, and water can also freeze into ice at a constant temperature. An ideal gas can also undergo isothermal expansion or compression. Here, an ideal gas in an isolated cylinder expands...

isochoric and isobaric processes

Constant Volume and Pressure in Thermodynamics

Thermodynamic processes can happen at constant volume or at constant pressure. An isochoric process is a constant-volume process. In this case, the volume does not change, so the work done by the system is zero. The first law of thermodynamics still applies, so any heat added or removed changes the internal energy of the system only. A simple example is heating 1000 g of water from 40 degrees celsius to 70 degrees celsius at constant volume. Because the process is isochoric, no work is done by...

heat capacities of an ideal gas i

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Ideal Gas Heat Capacity and Degrees of Freedom

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adiabatic processes for an ideal gas

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pressure and volume in an adiabatic process

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Free Expansion: Pressure, Volume, and Temperature

Free expansion shows how pressure, volume, and temperature behave when a gas expands without doing work. It is an adiabatic process, but it is not the same as adiabatic expansion. In free expansion, no work is done and the internal energy does not change. In adiabatic expansion, work is done and the internal energy changes. For an adiabatic process, the pressure-volume relation comes from the adiabatic condition. That relation does not apply to free expansion, even though the expansion is...

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Adiabatic Compression in an Engine Cylinder

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Using Maxwell's Relations in Thermodynamics

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joule-thomson effect

Gas Cooling and Heating in Throttling

Gas cooling and heating in throttling is explained by the Joule-Thomson effect, also called the Joule-Kelvin effect. It describes how a fluid changes temperature when it passes through a valve or porous plug in a thermally insulated system. This type of flow is called a throttling process. In the experiment, a high-pressure gas is forced through a throttle valve or porous plug into a lower-pressure region. The gas expands as it moves into the larger volume. Work is done on the gas as it is...

key terms and concepts

Learn how isothermal processes keep temperature constant while heat equals work during ideal gas expansion, with phase change and cylinder examples.

Isothermal Expansion and Heat Transfer | JoVE K12

physics

JoVE Core - Fisica apresenta a teoria e a aplicação de tópicos fundamentais da física, incluindo cinemática, dinâmica, mecânica dos fluidos, estática, ondas e acústica, com vídeos animados concisos e de fácil compreensão. Além disso, os vídeos de cientistas em ação demonstram a aplicação de conceitos relacionados em experimentos de pesquisa clássica e original realizados nos laboratórios de todo o mundo hoje em dia.

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New Jersey Student Learning Standards for Science

Physical Science

HS-PS3-1

Florida Department of Education

SC.912.P.10

SC.912.P.10.2

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New York State Science Learning Standards

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HS-PS3-3.

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HS-PS3-6

Isothermal Expansion and Heat Transfer

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