Name: le chatelier's principle in heating and cooling
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 19 s
Channel: JoVE

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Chemistry

Matter and its Interactions

PS.Chm.5.2

le-chatelier-s-principle-changing-temperature

Le Chatelier's Principle: Changing Temperature

온도는 화학 반응의 속도에 영향을 미칩니다. 따라서 평형 상태에서 반응에 대한 온도 변화는 시스템에 대한 부담으로 작용합니다. 르 샤틀리에의 원리에서는 이러한 장애를 최소화하기 위해 시스템이 어떻게 반응할 것인지를 예측합니다.

온도의 변화는 K의 값을 변화시키지 않고 평형을 이동시키는 농도나 부피의 변화와 달리 평형 상수의 값을 변화시킵니다. 오염화인 기체를 삼염화인과 염소 기체로 분해하는 반응을 고려해봅시다. 이 내열 반응의 경우 흡수된 열을 반응물이라고 생각할 수 있습니다.

온도가 증가하면 시스템에 열이 추가되는데 이는 반응물을 더 추가하는 것과 유사합니다. 따라서 평형 위치가 생성물 쪽으로 이동하며 더 많은 삼염화인과 염소를 생성하여 평형 상수 K의 값의 증가로 인한 여분의 열을 소비합니다. 다른 한편 온도가 낮아지면 시스템의 열이 제거되며 이는 반응물을 제거하는 것과 유사합니다.

평형 위치는 반응물 쪽으로 이동하며 더 많은 오염화인을 생성하여 K 값의 감소에 의하여 발생한 열을 방출합니다. 이산화황과 산소사이의 기체 반응으로 삼산화황을 생성하는 것과 같은 발열 반응의 경우, 방출되는 열은 하나의 생성물로 생각할 수 있습니다. 온도 상승은 생성물을 더 추가하는 것과 유사합니다.

이를 통해 평형 위치를 반응물 쪽으로 이동하게 되며 더 많은 아산화기체와 산소를 생성하여 K의 값의 감소로 인하여 발생한 열을 흡수합니다. 반대로, 이 발열 반응의 온도를 낮추면 열이 제거되여 생성물을 제거하는 것과 같습니다. 평형 위치는 생성물 쪽으로 이동하며 더 많은 삼산화 황을 생성하여 K가 증가함에 따라 발생한 열을 방출합니다.

따라서, 온도의 증가는 내열 반응에서 생성물을 선호하는 반면, 온도의 감소는 발열 반응에서 생성물을 선호합니다.

르 샤틀리에의 원리: 온도 변화

질량 작용의 법칙에 따라 농도 변화에 의해 응력을 받은 평형은 평형 상수 K 값의 변화 없이 평형을 다시 설정하기 위해 이동합니다. 그러나 온도 변화에 반응하여 평형이 이동하면 평형 상수에 대해 다른 값을 나타내는 다른 상대 조성으로 다시 설정됩니다.

이 현상을 이해하려면 기본 반응에 대해 생각해 보세요.

 <img alt="Eq1" src="/files/ftp_upload/11393/11393_Equation_1.png" style="height: 50px;" />

이는 기본 반응이므로 정방향 및 역방향 속도 법칙은 균형 방정식의 화학양론에서 직접 파생될 수 있습니다.

 <img alt="Eq2" src="/files/ftp_upload/11393/11393_Equation_2.png" style="height: 65px;" />

시스템이 평형 상태에 있을 때,

 <img alt="Eq3" src="/files/ftp_upload/11393/11393_Equation_3.png" style="height: 50px;" />

이 등식에 비율법칙을 대입하고 재배열하면 다음과 같습니다.

 <img alt="Eq4" src="/files/ftp_upload/11393/11393_Equation_4.png" style="height: 100px;" />

평형 상수는 정반응과 역반응에 대한 속도 상수의 수학적 함수로 표현될 수 있습니다. 아레니우스(Arrhenius) 방정식에 설명된 것처럼 속도 상수는 온도에 따라 달라지므로 평형 상수도 마찬가지로 온도에 따라 달라질 수 있습니다(속도 상수가 온도 변화에 따라 다양한 정도로 영향을 받는다고 가정). 다단계 반응 메커니즘을 포함하는 더 복잡한 반응의 경우 평형 상수와 메커니즘 단계의 속도 상수 사이에 유사하지만 더 복잡한 수학적 관계가 존재합니다. 반응이 얼마나 복잡하든 관계없이 평형 상수의 온도 의존성은 지속됩니다.

온도 변화에 반응하여 평형이 겪게 될 변화를 예측하는 것은 반응의 엔탈피 변화를 고려함으로써 가장 편리하게 수행됩니다. 예를 들어, 하버 과정에 의한 암모니아 형성은 발열(열 생성) 과정입니다.

 <img alt="Eq5" src="/files/ftp_upload/11393/11393_Equation_5.png" style="height: 50px;" />

르 샤틀리에의 원리를 적용할 목적으로 열 q는 생성물로 볼 수 있습니다.

 <img alt="Eq6" src="/files/ftp_upload/11393/11393_Equation_6.png" style="height: 50px;" />

시스템의 온도를 높이는 것은 제품의 양을 늘리는 것과 유사하므로 평형이 왼쪽으로 이동합니다. 시스템 온도를 낮추면 마찬가지로 평형이 오른쪽으로 이동합니다. 흡열 공정의 경우 열은 반응의 반응물로 간주되므로 반대의 온도 의존성이 관찰됩니다.

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">Openstax, Chemistry 2e, Section 13.3 Shifting Equilibria: Le </a><a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">Ch</a>â<a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">t</a><a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">elier’s Principle</a>.

질량 행동의 법칙에 따라 농도의 변화에 의해 강조되는 평형은 어떠한 변화도 없이 평형을 재확립하기 위해 변화할 것입니다.

Education

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Chemical Equilibrium

화학 평형

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 forward and reverse rate laws based on the balanced equation. At equilibrium, the forward and reverse reaction rates are equal. When those rate laws are combined and rearranged, the equilibrium constant can be expressed as a function of the forward and reverse rate constants.

Because rate constants change with temperature, as described by the Arrhenius equation, the equilibrium constant can also change with temperature. This idea applies to both elementary reactions and more complex multistep mechanisms. In multistep reactions, the math is more complicated, but the temperature dependence of the equilibrium constant still remains.

A practical way to predict the direction of the shift is to use the reaction’s enthalpy change. In the Haber process, ammonia formation is exothermic, which means it produces heat. For Le Chatelier's principle, heat can be treated like a product. Raising the temperature adds heat, so the equilibrium shifts left. Lowering the temperature removes heat, so the equilibrium shifts right. For endothermic processes, heat acts like a reactant, so the temperature effect is opposite.

Le Chatelier's Principle in Heating and Cooling

le-chateliers-principle-heating-and-cooling

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

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Relating Kc and Kp in Gas Equilibria

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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...

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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...

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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)

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

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...

le chatelier's principle: changing temperature

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 heating and cooling change chemical equilibrium, why K changes with temperature, and how exothermic and endothermic reactions shift.

Le Chatelier's Principle in Heating and Cooling | JoVE K12

chemistry

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Le Chatelier's Principle in Heating and Cooling

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