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

Tersine çevrilebilir bir kimyasal reaksiyon, reaktanların ürünlere dönüşümü ve ürünlerin tekrar reaktanlara dönüştürülmesinin aynı anda gerçekleştiği bir reaksiyondur. Reaktifler ve ürünler arasındaki çift ok, reaksiyonun tersinir doğasını gösterir. Ürünlerin oluşum hızı veya ileri reaksiyon hızı, reaktanların oluşum hızına veya ters reaksiyon hızına eşit olduğunda, kimyasal denge elde edilir.Kimyasal denge aslında dinamik bir süreçtir. Dışarıdan bakıldığında, tüm sistem statik görünür ancak moleküler düzeyde oldukça aktiftir. Fosfor pentaklorürün termal ayrışmasını düşünün.Kapalı bir kapta ısıtıldığında, gaz halindeki fosfor pentaklorür, geri dönüşümlü bir reaksiyonda fosfor triklorür ve klor gazı karışımına ayrışır. Reaksiyon ilerledikçe, fosfor pentaklorür konsantrasyonu azalırken, fosfor triklorür ve klor gazı artar. Sonuç olarak, ileri reaksiyonun hızı azalır ve ters reaksiyonun hızı artar.Sonunda, ileri ve geri reaksiyonların oranları eşitlenir ve sistem kimyasal dengeye ulaşır. Bu durumda, fosfor pentaklorür, fosfor triklorür ve klorun nispi konsantrasyonları artık değişmez. Böyle bir denge durumuna dinamik denge de denir çünkü hem ileri hem de ters reaksiyonlar aynı hızlarda gerçekleşmeye devam eder.Reaktanlar ve ürünler tüketildikleri gibi aynı oranlarda oluştukları için, konsantrasyonları eşit olmasa da sabit kalır. Kimyasal bir denge, belirli bir tersinir reaksiyondaki tüm reaktanlar ve ürünler aynı gaz veya sulu fazda ise, denge homojendir. Heterojen bir dengede, reaktanlar ve ürünler farklı fazlarda bulunur.

dinamik denge

Tersinir bir kimyasal reaksiyon, hem ileri (soldan sağa) hem de ters (sağdan sola) yönlerde ilerleyen kimyasal bir işlemi temsil eder. İleri ve geri reaksiyonların oranları eşit olduğunda, reaktan ve ürün türlerinin konsantrasyonları zaman içinde sabit kalır ve sistem dengededir. Reaksiyonun geri dönüşümlü doğasını vurgulamak için özel bir çift ok kullanılır. Denge sistemlerinde reaktanların ve ürünlerin nispi konsantrasyonları büyük ölçüde değişir; bazı sistemler çoğunlukla dengede ürünler içerir, bazıları çoğunlukla reaktan içerir ve bazıları her ikisinin de kayda değer miktarlarını içerir.
 
 Kimyasal Reaksiyonlarda Dinamik Denge
 
 Denklemde tanımlanan kahverengi nitrojen dioksiti elde etmek için renksiz dinitrojen tetroksidin tersine çevrilebilir ayrışmasını düşünün:
 
 <img alt=""Eq1"" src=""/files/ftp_upload/11385/11385_Equation_1.png"" style=""text-align: center; height: 50px;"" />
 
 Reaksiyon başladığında (zaman= 0), N2O 4reaktanının konsantrasyonu sonludur ve NO2 ürününün konsantrasyonu sıfırdır, bu nedenle ileri reaksiyon sonlu bir hızda ilerlerken ters reaksiyon hızı sıfırdır. Zaman geçtikçe, N2O4 tüketilir ve konsantrasyonu düşer, buna karşın NO2 üretilir ve konsantrasyonu artar. Reaktan konsantrasyonunun azalması ileri reaksiyon hızını azaltır ve artan ürün konsantrasyonu, ters reaksiyon hızını arttırır. Bu işlem, reaksiyonun dengeye ulaştığı ileri ve geri reaksiyon hızları eşit olana kadar devam eder. Kimyasal dengelerin dinamik olduğunu vurgulamak önemlidir; dengedeki bir reaksiyon “durmadı” ancak aynı hızda ileri ve geri yönlerde ilerler. Böylece, dengede N2O4 ve NO2 konsantrasyonları artık değişmez, çünkü NO2'nin oluşumu oranı, NO2'nin tüketim oranına tam olarak eşittir ve N2O4'ün oluşumu oranı, N2O4'ün tüketim hızına tam olarak eşittir.
 
 Homojen ve Heterojen Dengeler
 
 Homojen bir denge, aşağıdaki örneklerle gösterildiği gibi, tüm reaktanların ve ürünlerin (ve varsa herhangi bir katalizörün) aynı fazda, sıvı veya gaz fazında mevcut olduğu bir dengedir:
 
 <img alt=""Eq2"" src=""/files/ftp_upload/11385/11385_Equation_2.png"" style=""text-align: center; height: 90px;"" />
 
 Heterojen bir denge, reaktanları ve ürünleri aşağıdaki örnekte gösterildiği gibi iki veya daha fazla farklı fazda içerir:
 
 <img alt=""Eq3"" src=""/files/ftp_upload/11385/11385_Equation_3.png"" style=""text-align: center; height: 130px;"" />
 
 Bu metin bu kaynaktan uyarlanmıştır: <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>.

Dinamik Denge

Tersinir bir kimyasal reaksiyon, hem ileri (soldan sağa) hem de geri (sağdan sola) yönlerde ilerleyen kimyasal bir süreci temsil eder. Ne zaman...

Education

JoVE Core

Kimya

Chemical Equilibrium

Kimyasal Denge

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 Kimya, özlü ve kolay anlaşılır animasyon video derslerini kullanarak genel kimya kavramlarına hayat veriyor. Ek olarak, bilim insanı uygulama videolarımız ile klasik ve orijinal araştırma deneylerini dünya çapında günümüz laboratuvarlarında görselleştiriyoruz.

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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