Name: gas equilibrium under volume changes
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 32 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.2

le-chatelier-s-principle-changing-volume-pressure

Le Chatelier's Principle: Changing Volume (Pressure)

르 샤틀리에의 원리를 사용하여 평형 상태에 있는 시스템이 부피 또는 압력의 변화에 어떻게 반응하는지를 예측할 수 있습니다. 기체의 부피는 압력에 반비례합니다. 따라서 평형 상태에 있는 시스템의 경우 부피가 감소되면 압력이 증가되고 평형이 헝클어집니다.

이에 대응하여 평형 위치가 응력을 최소화하는 방향으로 이동합니다. 이상기체 법칙에 따르면 기체의 압력은 몰 수와 정비례합니다. 따라서 평형 회복에 필요한 이동 방향은 반응 양쪽에 있는 기체 입자의 몰 수에 따라 달라집니다.

기체의 몰이 많아지면 압력이 높아지기 때문에 압력이 증가하면 평형 위치가 몰이 적은 쪽으로 이동하여 압력을 낮춥니다. 마찬가지로, 압력이 감소하면 평형 위치가 기체의 몰 수가 많은 쪽으로 이동합니다. 한 몰의 오염화인 기체가 두 몰의 생성물, 즉 한 몰의 삼염화인과 한 몰의 염소 가스로 분해되는 화학 평형을 생각해 봅시다.

피스톤이 아래로 밀리면 평형 시스템의 부피가 감소하여 압력이 증가합니다. 이렇게 되면 평형이 파괴되고 Q가 K보다 커집니다. 따라서, 평형 위치는 압력을 낮추고 평형을 회복하기 위해 기체 입자의 몰이 더 적은 반응물 쪽으로 이동합니다.

반대로 피스톤을 위로 당기면 부피가 증가하고 압력이 감소합니다. 이 경우 Q는 K보다 작아집니다. 압력을 증가시키기 위해 평형 위치는 기체 몰 수가 많은 생성물 쪽으로 이동하여 평형을 회복합니다.

일정한 부피의 평형 혼합물에 불활성 기체를 추가하여 압력을 증가시키는 경우 기체 상태의 반응물 및 생성물의 부분적인 압력이 변하지 않기 때문에 평형에 영향을 주지 않습니다. 요오드 기체와 염소 기체가 반응하여 요오드 단일 염화물을 생성하는 것과 같은 기체 반응물 및 생성물의 수가 동일한 평형 시스템의 경우 시스템의 부피 변화는 평형성에 영향을 미치지 않습니다.

르 샤틀리에의 원리: 부피(압력) 변화

기체상 평형의 경우 반응물과 생성물의 농도 변화는 부피와 압력의 변화에 따라 발생할 수 있습니다. 이상기체의 분압 P는 몰농도 M에 비례합니다.

<img alt="Eq1" src="/files/ftp_upload/11392/11392_Equation 1.png" style="text-align: center; height: 70px;" />

따라서 반응물이나 생성물의 분압 변화는 본질적으로 농도 변화입니다. 그러므로 이러한 변화는 평형에 동일한 영향을 미칩니다. 반응물이나 생성물을 추가하거나 제거하는 것 외에도, 기체상 평형에서 화학종의 압력(농도)은 시스템이 차지하는 부피를 변경하여 변경할 수도 있습니다. 기체상 평형의 모든 화학종은 동일한 부피를 차지하므로, 부피의 변화가 발생하면 반응물과 생성물 모두에 대해 동일한 농도 변화가 발생합니다. 이러한 유형의 응력이 어떤 변화를 유발하는지 식별하려면 반응의 화학량론을 고려해야 합니다.

평형 상태에서 반응 N2 (g) + O2 (g) ⇌ 2 NO (g)는 반응 지수로 설명됩니다.

<img alt="Eq2" src="/files/ftp_upload/11392/11392_Equation 2.png" style="text-align: center; height: 70px;" />

이 종의 평형 혼합물이 차지하는 부피가 3배 감소하면 세 종 모두의 분압은 3배 증가합니다.

<img alt="Eq3" src="/files/ftp_upload/11392/11392_Equation 3.png" style="text-align: center; height: 70px;" />

따라서 이 기상 평형 혼합물의 부피를 변경해도 평형이 이동하지 않습니다.

그러나 다른 시스템인 2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g)를 유사하게 처리하면 다른 결과가 나타납니다.

<img alt="Eq4" src="/files/ftp_upload/11392/11392_Equation 4.png" style="text-align: center; height: 200px;" />

이 경우 부피 변화로 인해 반응 지수가 평형 상수보다 작아지므로 평형이 오른쪽으로 이동합니다.

이러한 결과는 기체상 평형의 화학량론과 부피로 인한 압력(농도) 변화 효과 사이의 관계를 보여줍니다. 첫 번째 예에서와 같이 반응물과 생성물의 총 몰량이 동일하면 부피 변화가 평형을 이동시키지 않습니다. 반응물과 생성물의 몰량이 다른 경우, 부피 변화는 부피 변화를 더 잘 "수용"하는 방향으로 평형을 이동시킵니다. 두 번째 예에서는 3몰의 반응물(SO2 및 O2)이 2몰의 생성물(SO3)을 생성하므로 시스템 부피를 줄이면 정반응이 (3몰) 역반응보다 더 적은 가스(2몰)를 생성하므로 평형이 오른쪽으로 이동합니다. 반대로, 이 평형 시스템의 부피를 늘리면 반응물로 이동하게 됩니다.

이 문서는 다음 링크에서 발췌되었습니다.

이 텍스트는 <a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">오픈 탁스, 화학 2e, 섹션 13.3 변속 평형에서 적응되었습니다 : LeChatelier의 원리</a>.

기체 상 평형의 경우, 반응물과 생성물의 농도 변화는 부피와 압력이 변경됨에 따라 발생할 수 있습니다. 분압 P, 의 ...

Education

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JoVE Core

화학

하나

Chemical Equilibrium

화학 평형

KEY TERMS AND CONCEPTS

주요 용어 및 개념

gas equilibrium under volume changes

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes.

When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change affects each species in the same way. To predict whether the equilibrium shifts, you must look at the reaction stoichiometry.

For the equilibrium N2(g) + O2(g) ⇌ 2 NO(g), decreasing the volume by a factor of 3 increases the partial pressures of all three gases by a factor of 3. In this case, the reaction quotient still matches the equilibrium position, so the equilibrium does not shift. The total moles of reactants and products are equal, and that is why the volume change has no effect.

A different result appears for 2 SO2(g) + O2(g) ⇌ 2 SO3(g). Here, decreasing the volume makes the reaction quotient smaller than the equilibrium constant, so the equilibrium shifts right. Three moles of reactant form two moles of product, so the forward reaction makes less gas. Increasing the volume would shift this system toward the reactants.

Gas Equilibrium Under Volume Changes

the equilibrium constant

Chemical Equilibrium and Kc Rules

Chemical equilibrium and the equilibrium constant Kc describe how reactants and products are balanced in a reaction. In the oxidation of sulfur dioxide, a mixture that starts with reactants only has no product at first. As the reaction moves forward toward equilibrium, reactant concentrations decrease and product concentration increases. When equilibrium is reached, the concentrations of both stay constant. A reaction can also begin with only products present. In that case, the reaction moves...

homogeneous equilibria for gaseous reactions

homogeneous-equilibria-for-gaseous-reactions

Relating Kc and Kp in Gas Equilibria

Gas-phase equilibrium can be written using either concentration or pressure. The equilibrium constant may be shown as Kc, which uses molar concentration, or as Kp, which uses partial pressure of the reactants and products. The link between Kc and Kp comes from the ideal gas equation and the definition of molarity. Molarity is the number of moles divided by volume. In the ideal gas equation, P stands for partial pressure, V for volume, n for number of moles, R for the gas constant, and T for...

le chatelier's principle: changing concentration

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Shifting Equilibrium by Changing Concentration

Chemical equilibrium is a dynamic balance. At equilibrium, the forward and reverse reactions happen at equal rates. If the system is stressed in a way that changes one rate more than the other, it is no longer at equilibrium and will shift until balance is restored. This behavior is described by Le Châtelier’s principle. Changes in concentration are a major stress on an equilibrium system. Reaction rates depend mainly on concentration and temperature. For that reason, changing the amount of a...

calculating the equilibrium constant

Finding Kc from Equilibrium Data

The equilibrium constant, Kc, can be found from the equilibrium concentrations of reactants and products. When those concentrations are known, the calculation is straightforward. The values are placed into the Kc expression for the reaction. One example uses nitrogen dioxide and dinitrogen tetroxide. When 0.10 mol NO2 is added to a 1.0-L flask at 25 °C, the concentrations change until equilibrium is reached. At equilibrium, [NO2] is 0.016 M and [N2O4] is 0.042 M, and these values are used to...

reaction quotient

Using Q to Track Equilibrium Changes

Reaction quotient Q helps track how far a reversible reaction has moved toward equilibrium. For a balanced reaction such as m A + n B ⇌ x C + y D, Q comes directly from the stoichiometric coefficients in the equation. When concentrations are used, the expression is written as Qc. For gases, a similar form uses partial pressures. These expressions use relative concentration and pressure values, not absolute values. That means reaction quotients are dimensionless and have no units. As a reaction...

dynamic equilibrium

Chemical Equilibrium in Reversible Reactions

Chemical equilibrium in reversible reactions happens when a reaction moves in both directions at the same time. A reversible reaction uses a double arrow to show that products can turn back into reactants. At equilibrium, the concentrations of reactants and products stay constant over time because the forward and reverse reaction rates are equal. The video uses the reversible decomposition of colorless dinitrogen tetroxide to brown nitrogen dioxide as an example. At time zero, there is finite...

calculating equilibrium concentrations

Equilibrium Concentrations from an ICE Table

Equilibrium concentrations can be found from initial concentrations and an equilibrium constant. This skill matters in many areas of science and technology, including pharmaceutical product formulation and dosing. After a drug is ingested or injected, it may take part in several chemical equilibria that change its final concentration in the body system of interest. Scientists use these quantitative equilibrium relationships to help calculate a dosage that will produce the desired therapeutic...

le chatelier's principle: changing volume (pressure)

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes. When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change...

le chatelier's principle: changing temperature

le-chatelier-s-principle-changing-temperature

Le Chatelier's Principle in Heating and Cooling

Le Chatelier's principle helps explain how chemical equilibrium responds to heating and cooling. A system at equilibrium will shift to restore balance after a temperature change, but the equilibrium constant, K, will not stay the same. Instead, the mixture reaches a new equilibrium with a different composition. This temperature effect is different from a concentration change, which shifts equilibrium without changing K. To understand why temperature matters, the reaction can be written with...

the small x assumption

Estimating Equilibrium with Small Changes

A small equilibrium constant can make equilibrium calculations easier. In these reactions, the equilibrium position favors the reactants. When the initial reactant concentration is high and the Kc value is small, the change in concentration may be negligible. In that case, the equilibrium concentration is close to the initial concentration. This idea helps simplify weak acid and weak base problems. Chemists can assume that some equilibrium concentrations are equal to the initial concentrations.

key terms and concepts

Learn how changing volume changes pressure and concentration in gas-phase equilibrium, and why stoichiometry decides whether the system shifts left or right.

Gas Equilibrium Under Volume Changes | JoVE K12

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Gas Equilibrium Under Volume Changes

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