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

التفاعل الكيميائي التعاكسي،هو تفاعل،تحوّل للمواد المتفاعلة إلى نواتج وتحول عكسي للنواتج إلى مواد متفاعلة،بشكل متزامن. يوضع سهم مزدوج بين المواد المتفاعلة وبين النواتج للدلالة على طبيعتها التعاكسية. عندما يتساوى معدل تشكيل النواتج،أو معدل سرعة التفاعل إلى الأمام،مع معدل تكوين المواد المتفاعلة،أو معدل سرعة التفاعل العكسي يتحقق التوازن الكيميائي.التوازن الكيميائي في الواقع عملية ديناميكية. يبدو النظام بأكمله ساكنًا من الخارج-غير أنه على المستوى الجزيئي نشط جدًا. لنتأمل التفكك الحراري لخماسي كلوريد الفوسفور.عند تسخينه داخل وعاء مغلق،يتفكك غاز خماسي كلوريد الفوسفور إلى مزيج من ثلاثي كلوريد الفوسفور وغاز الكلور في تفاعل تعاكسي. مع تواصل حدوث التفاعل،يقل تركيز خماسي كلوريد الفوسفور فيما يزداد تزداد كمية ثلاثي كلوريد الفوسفور وغاز الكلور. ونتيجة لذلك،فإنّمعدل التفاعل الأمامي ينخفض بينما معدل التفاعل العكسي يرتفع.وأخيرًا،يتساوي معدل سرعتي التفاعل الأمامي و العكسي،ويحقق النظام توازنًا كيميائيًا. في هذه الحالة،فإن التركيزات النسبية لخماسي كلوريد الفوسفور،وثلاثي كلوريد الفوسفور،والكلور،لم تعد تتغير. مثل حالة التوازن هذه تسمى كذلك،توازنًا ديناميكيًا لأن كلا التفاعلين الأمامي والعكسي يتواصل حدوثهما ولكن بنفس معدل السرعة.بما أن المواد المتفاعلة والنواتج تتشكل بنفس المعدلات التي تُستهلك بها،فإنّتركيزاتها تبقى ثابتة،وليس بالضرورة متساوية. يكون التوازن الكيميائي متجانسًا،إذا كانت جميع المواد المتفاعلة والنواتج في تفاعل تعاكسي معيّن في الحالة ذاتها إما الغازية وإما السائلة. أما في التوازن غير المتجانس،فتكون المواد المتفاعلة والنواتج في حالات مختلفة.

التوازن الديناميكي

يمثل التفاعل الكيميائي القابل للانعكاس عملية كيميائية تستمر في الاتجاهين الأمامي (من اليسار إلى اليمين) والعكس (من اليمين إلى اليسار). عندما تكون معدلات التفاعلات الأمامية والعكسية متساوية، فإن تركيزات المادة المتفاعلة والمنتج تظل الأنواع ثابتة بمرور الوقت ويكون النظام في حالة توازن. يتم استخدام سهم مزدوج خاص للتأكيد على الطبيعة القابلة للانعكاس للتفاعل.تختلف التركيزات النسبية للمواد المتفاعلة والمنتجات في أنظمة التوازن بشكل كبير ؛ تحتوي بعض الأنظمة في الغالب على منتجات في حالة توازن ، وبعضها يحتوي على معظمها مواد متفاعلة ، وبعضها يحتوي على كميات ملحوظة من كليهما. التوازن الديناميكي في التفاعلات الكيميائية ضع في اعتبارك التحلل العكسي لرباعي أكسيد ثنائي النيتروجين عديم اللون لإنتاج ثاني أكسيد النيتروجين البني، كما هو موضح في المعادلة: <img alt="Eq1" src="/files/ftp_upload/11385/11385_Equation_1.png" style="text-align: center; height: 50px;" /> عندما يبدأ التفاعل (الوقت = 0) ، يكون تركيز المادة المتفاعلة N2O4 محدوداً وتركيز المنتج NO2 هو صفر، لذلك يستمر التفاعل الأمامي بمعدل محدود بينما يكون معدل التفاعل العكسي صفراً. مع مرور الوقت ، يتم استهلاكN2O4 وينخفض ​​تركيزه ، بينما ينتج NO2 ويزداد تركيزه. يؤدي انخفاض تركيز المادة المتفاعلة إلى إبطاء معدل التفاعل الأمامي ، كما يؤدي تركيز المنتج المتزايد إلى تسريع معدل التفاعل العكسي. تستمر هذه العملية حتى تتساوى معدلات التفاعل الأمامية والعكسية، وفي ذلك الوقت يصل التفاعل إلى التوازن. من#8217; المهم التأكيد على أن التوازن الكيميائي ديناميكي ؛ وإن تفاعل ما عند التوازن لم “يتوقف,” لكنه يسير في الاتجاهين الأمامي والخلفي بنفس المعدل. وبالتالي، عند التوازن، لم تعد تركيزات N2O4 و NO2 تتغير لأن معدل تكوين NO2 يساوي تمامًا معدل استهلاك NO2، ومعدل تكوين N2O4 يساوي تمامًا بمعدل استهلاك N2O4.التوازن متجانس وغير متجانس التوازن المتجانس هو التوازن الذي توجد فيه جميع المواد المتفاعلة والمنتجات (وأي محفزات ، إن أمكن) في نفس المرحلة، إما في الطور المائي أو الغازي، كما هو موضح في الأمثلة التالية: <img alt="Eq2" src="/files/ftp_upload/11385/11385_Equation_2.png" style="text-align: center; height: 90px;" /> يشتمل التوازن غير المتجانس على المواد المتفاعلة والمنتجات في مرحلتين مختلفتين أو أكثر ، كما هو موضح في المثال التالي: <img alt="Eq3" src="/files/ftp_upload/11385/11385_Equation_3.png" style="text-align: center; height: 130px;" />تم اقتباس هذا النص من <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>.

يمثل التفاعل الكيميائي القابل للانعكاس عملية كيميائية تسير في كل من الاتجاهين الأمامي (من اليسار إلى اليمين) والخلف (من اليمين إلى اليسار). متى...

Education

JoVE Core

الكيمياء

واحد

Chemical Equilibrium

الاتزان الكيميائي

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

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.

Scientific Laws and Theories

Scientific Laws

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The Scientific Method

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Classifying Matter by State

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Classifying Matter by Composition

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The Atomic Theory of Matter

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Subatomic Particles

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Elements: Chemical Symbols and Isotopes

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PS.Chm.1.1

Radioactivity and Nuclear Equations

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Nuclear Binding Energy

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Radioactive Decay and Radiometric Dating

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Nuclear Fission

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Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

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Nuclear Transmutation

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Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

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The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

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electron-configuration-of-multielectron-atoms

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The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

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Molar Mass

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Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

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Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

Types of Chemical Bonds

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Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

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The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

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Resonance

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Formal Charges

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Exceptions to the Octet Rule

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	...

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

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Intermolecular vs Intramolecular Forces

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Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

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Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Chemical Equilibrium in Reversible Reactions

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