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

시스템 내부 또는 외부에서 열 전달이 없는 열역학적 과정을 단열이라고 합니다.
따라서 열역학 제1법칙에 따르면 내부 에너지의 변화는 단열 과정에서 수행된 작업의 음수입니다.
예를 들어, 단열 튜브로 구성된 화재 피스톤은 한쪽 끝이 닫혀 있고 다른 쪽 끝에는 움직일 수 있는 플런저가 있습니다. 
작은 면봉 조각을 튜브 안에 넣고 플런저를 실온에서 빠르게 밀어 내리면 열이 가해지지 않아도 면봉에 불이 붙습니다. 이것은 단열 압축으로 인해 발생합니다.
여기서, 부피가 감소함에 따라 수행된 작업은 음수가 됩니다. 따라서 내부 에너지 변화는 양수이며 그에 따라 가스 온도가 증가합니다.
반대로, 냉각된 탄산 음료 병을 열 때 병에 갇힌 가스는 단열 팽창을 겪어 작업이 긍정적으로 수행됩니다.
그 결과, 내부 에너지는 해당 온도 강하에 따라 감소하여 증발된 증기를 눈에 보이는 구름으로 응축합니다.

<ol>
	<li>Young, H.D. 및 Freedman, RA (2012). 현대 물리학을 가진 대학 물리학. 샌프란시스코, 캘리포니아 : 피어슨. 640쪽.</li>
	<li>오픈스택스. (2019). 대학 물리학 Vol. 2. [웹 버전]. 원본 주소 <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>

이상기체의 단열과정

이상 기체를 단열 압축하면, 즉 열을 가하지 않고 압축하면 작업이 수행되어 온도가 상승합니다. 단열 팽창에서는 가스가 작동하고 온도가 떨어집니다. 단열 압축은 실제로 자동차의 실린더에서 발생하는데, 여기서 가스-공기 혼합물의 압축이 너무 빨리 일어나서 혼합물이 주변 환경과 열을 교환할 시간이 없습니다. 그럼에도 불구하고 압축 중에 혼합물에 작업이 수행되기 때문에 혼합물의 온도가 크게 상승합니다. 실제로 온도 상승이 너무 커서 불꽃을 추가하지 않고도 혼합물이 폭발할 수 있습니다. 그러한 폭발은 시간이 정해져 있지 않기 때문에 자동차의 운행을 제대로 하지 못하게 만듭니다. 보통은 '노크'를 합니다. 휘발유의 옥탄가에 따라 발화 온도가 높아지는 만큼 옥탄가가 높은 휘발유를 사용하는 것도 이러한 문제를 극복하는 한 가지 방법입니다.

또 다른 흥미로운 단열 과정은 기체의 자유 팽창입니다. 가스가 2개의 격실로 구성된 단열 용기의 한 면에 막으로 갇혀 있다고 상상해 보십시오. 막에 구멍이 뚫리면 가스가 용기의 빈 쪽으로 돌진하여 자유롭게 팽창합니다. 가스가 '진공에 대해' 팽창하면 압력이 감소하고(p = 0) 아무런 일도 하지 않으며, 용기가 단열되어 있기 때문에 팽창은 단열됩니다. 첫 번째 법칙에서 Q = 0 및 W = 0이면 dU = 0이므로 초기 및 최종 평형 상태의 내부 에너지는 다음과 같습니다. 무료 확장도 마찬가지입니다. 이상적인 기체라면 내부 에너지는 온도에만 의존합니다. 따라서 이상기체가 자유롭게 팽창할 때 온도는 변하지 않습니다.

이상 기체가 단열적으로 압축되면 열을 가하지 않고 작업이 수행되고 온도가 상승합니다. 단열 확장에서 ...

Education

교육

JoVE Core

Physics

물리학

Unit 1

제1단원

The First Law of Thermodynamics

열역학 제1법칙

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

gas-temperature-changes-in-adiabatic-processes

thermodynamic systems

Open, Closed, and Isolated Systems

A thermodynamic system is the part of the world that scientists study for its heat and energy behavior. It sits inside a surrounding environment, or surroundings. The system and the surroundings can exchange heat and do work across the boundary that separates them. The immediate surroundings affect the system most strongly because they interact with it directly. A kettle of boiling tea shows how this works in everyday life. The tea and the kettle together form the system. If the lid is open,...

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Gas Work in a Piston Cylinder

Gas work in a piston cylinder describes how pressure and volume change are related in thermodynamics. In mechanics, work happens when a force moves an object. In thermodynamics, work done on a system can be estimated when the system changes volume during a process. A gas can be trapped in a cylinder with a movable piston at one end. When the gas expands from volume V1 to volume V2, it pushes on the piston and moves it by a small distance dr. If the pressure on the piston face is p and the...

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Path Dependence in Gas Work

Work done by an ideal gas can depend on the path it takes between two thermodynamic states. The transcript compares two routes from state A to state C for the same gas. In both cases, the gas expands from volume V1 to volume V2, but the work is not the same. Along path AC, the gas stays at constant temperature T. It expands from V1 to V2. The work done by the gas is found from the pressure-volume relation for an ideal gas. After substituting pressure as nRT/V and integrating, the work for this...

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Two Gas Paths to the Same Volume

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internal energy

How Internal Energy Changes in Gas Systems

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Net Work in a Cyclic Thermodynamic Process

A cyclic thermodynamic process returns a system to its initial state. In a cycle, the change in internal energy is zero. An isolated system is different because it has zero heat exchange and zero work, so its internal energy stays constant. For a non-isolated system, the internal energy change is zero only when the process is cyclic. The first law of thermodynamics relates internal energy, heat transfer, and work. It states that the change in internal energy is the difference between the net...

isothermal processes

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...

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

Ideal Gas Heat Capacity at Constant Pressure

Heat capacity describes how much heat a substance absorbs for a given change in temperature. It is also called thermal capacity, and its SI unit is J/K. Specific heat capacity is the heat needed to raise the temperature of 1 kg of a substance by 1 K, and its SI unit is J/kg·K. The video also explains molar heat capacity. This is the amount of heat added or removed to change the temperature of 1 mole of a substance by 1 K. It can be measured at constant volume or constant pressure, and it is...

heat capacities of an ideal gas ii

Ideal Gas Heat Capacity Differences

Ideal gas heat capacities depend on whether the gas is heated at constant volume or constant pressure. At constant volume, the heat absorbed only raises the internal energy of the system. No work is done in this case. At constant pressure, the situation is different. The heat absorbed increases the internal energy and also does work. Molar heat capacity is the heat needed to raise the temperature of 1 mole of gas by 1 unit. Because some of the added heat goes into work, more heat is needed at...

heat capacities of an ideal gas iii

Ideal Gas Heat Capacity and Degrees of Freedom

Ideal gas heat capacity depends on degrees of freedom, which are the independent ways a gas molecule can move, rotate, and vibrate. If d is the number of degrees of freedom, the molar heat capacity at constant volume can be written in terms of d. The molar heat capacity at constant pressure can also be written using the relationship between the two heat capacities. The ratio of molar heat capacity at constant pressure to molar heat capacity at constant volume is called the ratio of heat...

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

pressure-and-volume-in-an-adiabatic-process

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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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...

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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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