Name: chemical equilibrium in reversible reactions
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 20 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.2

Dynamic Equilibrium

가역 화학 반응은 반응물을 생성물로 변환하는 생성물을 반응물로 변환하는 반응이 동시에 발생하는 반응입니다. 반응물과 생성물사이의 이중 화살표는 그 가역성을 나타냅니다. 생성물의 형성 속도 또는 정반응 속도가 반응물의 형성 속도 또는 역반응 속도와 같으면 화학적 평형이 달성됩니다.

화학 평형은 사실 역동적인 과정입니다. 외부에서 들여다보면 전체 시스템이 정적인 상태로 보이지만 분자 수준에서는 매우 활동적입니다. 오염화인의 열 분해 과정을 고려해봅시다.

기체 상태의 오염화인은 밀폐된 용기 안에서 가열될 때 역반응에 의해 삼염화인과 염소 기체 혼합물로 분해됩니다. 반응이 진행됨에 따라 오염화인의 농도는 감소하는 반면 삼염화인과 염소 기체는 증가합니다. 그 결과 정반응 속도는 감소하고 역반응 속도는 증가합니다.

결국, 정반응과 역반응의 속도는 같아지고, 시스템은 화학적 평형을 달성합니다. 이 상태에서, 오염화인, 삼염화인, 염소의 상대적 농도는 더 이상 변하지 않습니다. 이러한 평형 상태는 정반응 및 역반응이 계속 발생하지만 동일한 속도를 가지기 때문에 동적 평형이라고도 합니다.

반응물과 생성물은 소비된 것과 동일한 속도로 형성되기 때문에 반드시 동일하지는 않더라도 농도는 일정하게 유지됩니다. 기체든 액체든 주어진 역반응의 모든 반응물과 생성물이 같은 단계에 있다면 화학 평형은 균일합니다. 불규일 평형에서는 반응물과 생성물이 서로 다른 상으로 존재합니다.

동적 평형

가역적 화학 반응은 정방향(왼쪽에서 오른쪽)과 역방향(오른쪽에서 왼쪽)으로 진행되는 화학 과정을 나타냅니다. 정반응과 역반응의 속도가 같을 때, 반응물과 생성물 종의 농도는 시간이 지나도 일정하게 유지되고 시스템은 평형 상태에 있게 됩니다. 반응의 가역적 특성을 강조하기 위해 특수 이중 화살표가 사용됩니다. 평형 시스템에서 반응물과 생성물의 상대적 농도는 크게 다릅니다. 일부 시스템에는 대부분 평형 상태의 생성물이 포함되어 있고, 일부 시스템에는 대부분 반응물이 포함되어 있으며, 일부 시스템에는 상당한 양의 두 가지가 모두 포함되어 있습니다.

화학 반응의 동적 평형

무색 사산화이질소가 가역적으로 분해되어 갈색 이산화질소를 생성하는 방정식을 생각해 보십시오.

<img alt="Eq1" src="/files/ftp_upload/11385/11385_Equation_1.png" style="text-align: center; height: 50px;" />

반응이 시작되면(시간 = 0) N_2O_4 반응물의 농도는 유한하고 NO_2 생성물의 농도는 0이므로 정반응은 유한한 속도로 진행되고 역반응 속도는 0이 됩니다. 시간이 지남에 따라 N_2O_4는 소비되어 농도가 낮아지고, NO_2는 생성되어 농도가 증가합니다. 반응물의 농도가 감소하면 정반응 속도가 느려지고, 생성물 농도가 증가하면 역반응 속도가 빨라집니다. 이 과정은 정반응 속도와 역반응 속도가 동일해질 때까지 계속되며, 이때 반응은 평형에 도달합니다. 화학적 평형은 역동적이라는 점을 강조하는 것이 중요합니다. 평형 상태에서의 반응은 "멈추지" 않았지만 정방향과 역방향으로 같은 속도로 진행됩니다. 따라서 평형 상태에서는 NO_2의 생성 속도가 NO_2의 소비 속도와 정확히 같고, N_2O_4의 생성 속도는 N_2O_4의 소비 속도와 정확히 같기 때문에 N2O4와 NO_2의 농도는 더 이상 변하지 않습니다.

동종 및 이종 평형

균질 평형은 다음 예에서 설명하는 것처럼 모든 반응물과 생성물(및 적용 가능한 경우 모든 촉매)이 수성 또는 기상의 동일한 상에 존재하는 평형입니다.

<img alt="Eq2" src="/files/ftp_upload/11385/11385_Equation_2.png" style="text-align: center; height: 90px;" />

이종 평형은 다음 예에서 설명하는 것처럼 두 개 이상의 서로 다른 위상에 있는 반응물과 생성물을 포함합니다.

<img alt="Eq3" src="/files/ftp_upload/11385/11385_Equation_3.png" style="text-align: center; height: 130px;" />

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/13-1-chemical-equilibria">Openstax, Chemistry 2e, Section </a><a href="https://openstax.org/books/chemistry-2e/pages/13-1-chemical-equilibria">13.1 Chemical Equilibria</a>.

가역적 화학 반응은 정방향(왼쪽에서 오른쪽으로)과 역방향(오른쪽에서 왼쪽으로)으로 진행되는 화학 과정을 나타냅니다. 언제...

Education

교육

JoVE Core

화학

하나

Chemical Equilibrium

화학 평형

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 N2O4 and no NO2, so the forward reaction begins while the reverse reaction is still zero. As N2O4 is used up, its concentration falls. As NO2 forms, its concentration rises.

These concentration changes affect the reaction rates. Less N2O4 slows the forward reaction, and more NO2 speeds the reverse reaction. The process continues until both rates match. At that point, the system has reached equilibrium.

Chemical equilibrium is dynamic, not stopped. The reaction still proceeds in both directions, but at the same rate. So the amount of NO2 does not change because it is formed and consumed at equal rates, and the amount of N2O4 stays constant for the same reason.

The video also distinguishes homogeneous and heterogeneous equilibria. A homogeneous equilibrium has all reactants and products in the same phase, such as all aqueous or all gaseous species. A heterogeneous equilibrium has reactants and products in two or more different phases.

Chemical Equilibrium in Reversible Reactions

chemical-equilibrium-in-reversible-reactions

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

le-chatelier-s-principle-changing-concentration

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 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)

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-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 reversible reactions reach chemical equilibrium, why it is dynamic, and how homogeneous and heterogeneous equilibria differ in high school chemistry.

Chemical Equilibrium in Reversible Reactions | JoVE K12

chemistry

JoVE Core 화학은 간결하고 이해하기 쉬운 애니메이션을 통해 일반 화학 개념을 설명합니다. 또한, 과학자가 직접 고전실험과 연구실험을 진행하는 실사 영상을 제공합니다.

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.F

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-2

HS-PS1-6

HS-PS1-7

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Arizona Science Standards

HS+C.P1

HS+C.P1U1.6

Next Generation Science Standards

Matter and Its Interactions

Florida Department of Education

SC.912.P.12

SC.912.P.12.13

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS1-2

C-PS1-6

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-6.

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Chemical Equilibrium in Reversible Reactions

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