Name: using q to track equilibrium changes
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 35 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

Reaction Quotient

Denge sabiti ifadesi, her birinin kendi stokiyometrik katsayıları üssü olarak alınmış, ürünler C ve D molar konsantrasyonları bölü dengedeki A ve B reaktanları olarak yazılır. Çözüldüğünde, ifade denge sabiti Kc'ye eşit olacaktır. Herhangi bir konsantrasyondaki reaktanlar ve ürünler için aynı formda bir ifade de yazılabilir ve hesaplanan miktar reaksiyon katsayısı, Qc, olarak bilinir.Qc gibi, Qp ifadesi de kısmi basınçlar kullanılarak gaz reaksiyonları için yazılabilir. K, konsantrasyondan bağımsız olarak belirli bir sıcaklıkta sabit kalırken, reaksiyon ürünlere veya reaktanlara doğru ilerledikçe Q'nun değeri değişir. Reaksiyon katsayısı, dengeye ulaşmak için bir reaksiyonun ilerleyeceği yönü belirlemek için kullanılabilir.Belirli bir reaksiyonun başlangıcında, ürünlerin konsantrasyonu sıfır ise, reaksiyon katsayısı sıfırdır. Paydadaki reaktanların konsantrasyonu yüksek olduğunda, yani Q, K'den küçükse, reaksiyon, sistem dengeye ulaşana kadar daha fazla ürün sentezlemek için sağa hareket edecektir. Reaktanların konsantrasyonu sıfır ise, reaksiyon katsayısı sonsuzdur.Paydaki ürünlerin konsantrasyonu yüksek olduğunda, Q, K'den daha büyükse, reaksiyon sola kayarak daha fazla reaktan üretecektir. Q, K'ye eşitse, sistem dengededir ve ileri ve geri reaksiyonların hızı eşittir. Denge sabiti 50 verilen reaksiyonu düşünün.Reaksiyon karışımı 0, 20 molar hidrojen, 0, 20 molar iyot ve 1, 7 molar hidrojen iyodür içeriyorsa, gösterilen reaksiyonun yönü Q'nun hesaplanmasıyla belirlenebilir. Verilen konsantrasyonları ifadeye koyarsak, Q 72'ye eşittir ki bu K'dan büyüktür. Bu nedenle, tepkime sola doğru kayacaktır.

<ol>
	<li>Lederer, Robert. "Denge Problemlerini Çözmek İçin Reaksiyon Katsayısı Gereksizdir: Q ile İlgili Sorun Yok." Kimya Eğitimi Dergisi 82, no. 8 (2005): 1149. <a href="https://pubs.acs.org/doi/pdf/10.1021/ed082p1149.2">https://pubs.acs.org/doi/pdf/10.1021/ed082p1149.2</a></li>
</ol>

reaksiyon katsayısı

Tersinir bir reaksiyonun durumu, reaksiyon katsayısı (Q) değerlendirilerek uygun şekilde belirlenir. m A + n B ⇌ x C + y D tarafından tanımlanan tersinir bir reaksiyon için, reaksiyon katsayısı doğrudan dengeli denklemin stokiyometrisinden türetilir
 
 <img alt=""Eq1"" src=""/files/ftp_upload/11389/11389_Equation_1.png"" style=""text-align: center; height: 90px;"" />
 
 Burada alt simge c, ifadede molar konsantrasyonların kullanımını gösterir. Eğer reaktanlar ve ürünler gaz halinde ise, kısmi basınçlar kullanılarak bir reaksiyon bölümü benzer şekilde türetilebilir:
 
 <img alt=""Eq2"" src=""/files/ftp_upload/11389/11389_Equation_2.png"" style=""text-align: center; height: 90px;"" />
 
 Yukarıdaki reaksiyon katsayısı denklemlerinin,mutlak değerleri yerine konsantrasyonlar ve basınçlar için göreceli değerlerini kullanan daha titiz ifadelerin basitleştirilmesi olduğunu unutmayın. Bu nispi konsantrasyon ve basınç değerleri boyutsuzdur (birimleri yoktur); sonuç olarak, reaksiyon katsayıları da öyledir.
 
 Q 'nun sayısal değeri, reaksiyon dengeye doğru ilerlerken değişir; bu nedenle, reaksiyonun durumunun yararlı bir göstergesi olarak hizmet edebilir. Bu noktayı açıklamak için sülfür dioksitin oksidasyonunu düşünün:
 
 <img alt=""Eq3"" src=""/files/ftp_upload/11389/11389_Equation_3.png"" style=""text-align: center; height: 50px;"" />
 
 Burada iki farklı deneysel senaryo mümkündür, bunlardan biri bu reaksiyonun sadece reaktanların bir karışımı ile başlatıldığı, yani SO2 ve O2 ve diğeri sadece bir ürünle başlayan, yani SO3. Sadece reaktanların bir karışımı ile başlayan reaksiyon için, Q başlangıçta sıfıra eşittir:
 
 <img alt=""Eq4"" src=""/files/ftp_upload/11389/11389_Equation_4.png"" style=""text-align: center; height: 90px;"" />
 
 Reaksiyon ileri yönde dengeye doğru ilerledikçe, reaktan konsantrasyonları azalır (QC paydası gibi), ürün konsantrasyonu artar (QC paydası gibi) ve sonuç olarak reaksiyon katsayısı artar. Denge sağlandığında, reaktanların ve ürünün konsantrasyonları, QCdeğeri gibi sabit kalır.
 
 Eğer reaksiyon sadece ürün ile başlıyorsa, QC değeri başlangıçta tanımlanmamıştır (ölçülemez derecede büyük veya sonsuz):
 
 <img alt=""Eq5"" src=""/files/ftp_upload/11389/11389_Equation_5.png"" style=""text-align: center; height: 90px;"" />
 
 Bu durumda, reaksiyon ters yönde dengeye doğru ilerler. Ürün konsantrasyonu ve QC payları zamanla azalır, reaktan konsantrasyonları ve QC paydası artar ve reaksiyon katsayısı dengede sabit hale gelene kadar azalır. Bir sistem tarafından dengede sergilenen Q 'nun sabit değerine denge sabiti denirK:
 
 <img alt=""Eq6"" src=""/files/ftp_upload/11389/11389_Equation_6.png"" style=""text-align: center; height: 50px;"" />
 
 Reaksiyon Katsayılarının Değerlendirilmesi
 
 Gaz halindeki azot dioksit bu denkleme göre dinitrojen tetroksit oluşturur:
 
 <img alt=""Eq7"" src=""/files/ftp_upload/11389/11389_Equation_7.png"" style=""text-align: center; height: 50px;"" />
 
 1,0 L'lik bir flaska 25 °C 'de 0,10 mol NO2 eklendiğinde, konsantrasyon dengede [NO2] = 0,016 M ve [N2O4] = 0,042 M olacak şekilde değişir. Herhangi bir ürün oluşmadan önce, [NO2] = 0,10 M ve [N2O4] = 0 M. Dolayısıyla,
 
 <img alt=""Eq8"" src=""/files/ftp_upload/11389/11389_Equation_8.png"" style=""text-align: center; height: 90px;"" />
 
 Dengede,
 
 <img alt=""Eq9"" src=""/files/ftp_upload/11389/11389_Equation_9.png"" style=""text-align: center; height: 90px;"" />
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href=""https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants"">Openstax, Chemistry 2e, Section 13.2 Equilibrium Constants</a><a href=""https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants"">.</a>

Reaksiyon Katsayısı

Tersinir bir reaksiyonun durumu, reaksiyon katsayısı (Q) değerlendirilerek uygun bir şekilde değerlendirilir. m A + n B ile tanımlanan tersinir bir reaksiyon için ...

Education

JoVE Core

Kimya

Chemical Equilibrium

Kimyasal Denge

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 moves toward equilibrium, the value of Q changes, so it gives a snapshot of the system’s status.

The oxidation of sulfur dioxide shows how Q changes over time. If a reaction starts with only reactants, SO2 and O2, then Q is initially zero. As the reaction moves forward, reactant concentrations drop, the denominator of Qc gets smaller, product concentration rises, and Qc increases.

If the reaction starts with only product, SO3, then Qc is initially undefined and can be treated as immeasurably large or infinite. In that case, the reaction moves in reverse toward equilibrium. Product concentration and the numerator of Qc decrease, while reactant concentrations and the denominator increase. Qc keeps dropping until it becomes constant at equilibrium.

The constant value of Q for a system at equilibrium is the equilibrium constant, K. A nitrogen dioxide example shows how this works in practice. When 0.10 mol NO2 is placed in a 1.0-L flask at 25 °C, the initial concentrations are [NO2] = 0.10 M and [N2O4] = 0 M, so Qc can be found from the starting amounts. At equilibrium, [NO2] = 0.016 M and [N2O4] = 0.042 M, and Qc is calculated again from those concentrations.

Using Q to Track Equilibrium 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

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

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)

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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 the reaction quotient Q shows whether a reversible reaction is moving forward, reversing, or reaching equilibrium using concentration and pressure examples.

Using Q to Track Equilibrium Changes | JoVE K12

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Matter And Its Interactions

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Using Q to Track Equilibrium Changes

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