Name: shifting equilibrium by changing concentration
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 27 s
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Le Chatelier's Principle: Changing Concentration

يكون النظام في حالة توازن ديناميكي،حين يكون معدل سرعة التفاعل الأمامي مساوية لمعدل سرعة التفاعل العكسي. مع أن التفاعل لا يزال مستمرًا في كلا الاتجاهين،فإن التركيزات الإجمالية للمواد المتفاعلة والنواتج تبقى ثابتة. عند هذه النقطة،إذا تغير تركيز مادة متفاعلة أو ناتج،على سبيل المثال بإضافة جزيء إضافي من A أو بإزالة بعض جزيئات من C،يختل التوازن.مثل هذه التغيرات تشكل اختلالات في النظام. وفقًا لمبدأ لو شاتليه،عندما يختل نظام في حالة توازن،نتيجة تغيير في التركيز،أو الحجم،أو الضغط،أو درجة الحرارة،سيتغير التوازن في الاتجاه الذي يحد من الاختلال ويستعيد التوازن. لفهم ردة فعل النظام للتغييرات في التركيز،لنتأمل خزاني مياه متصلين،و مبدئيًا يكون مستوى الماء في الخزانين متساوي،ويكون النظام في حالة توازن.ثم يُضاف الماء إلى الخزان يرتفع مستوى الماء في الخزان نتيجة الاختلال فيختل التوازن. لموازنة هذا الاختلال،يتدفق جزء من الماء إلى الخزان لاستعادة التوازن. وفي المقابل،إذا أزيل ماء من الخزان فإن انخفاض مستوى الماء يسبب اختلالًا.وبالتالي يتدفق الماء من الخزان إلى الخزان لاستعادة التوازن. بالنسبة لنظام في حالة توازن يكون حاصل قسمة التفاعل مساويًا لثابت التوازن. بإضافة مزيد من المواد المتفاعلة إلى خليط التوازن،تنخفض قيمة Q.وفقًا لمبدأ لو شاتليه،فإن النظام يحد من هذا الاختلال بتحريك وضعية التوازن نحو النواتج لاستهلاك المادة الفاعلةالمضافة واستعادة التوازن.وبالمثل،فإن إزالة منتج من الخليط المتوازن ستؤدي إلى ردة فعل مشابهة من أجل استعادة التوازن. وعلى العكس،فإن إضافة مزيد من النواتج تزيد قيمة Q،وبالتالي،تتحرك وضعية التوازن باتجاه المواد المتفاعلة لاستهلاك الناتج المضاف واستعادة التوازن. إذا طرأ تغيير على التركيز ستتحرك وضعية التوازن دون تغيير قيمة K.

مبدأ لوشاتيليير: تغيير التركيز

يكون النظام في حالة توازن في حالة توازن ديناميكي ، مع حدوث تفاعلات أمامية وعكسية بمعدلات متساوية. إذا تعرض نظام التوازن لتغيير في الظروف التي تؤثر على معدلات التفاعل هذه بشكل مختلف (إجهاد ) ، فإن المعدلات لم تعد متساوية والنظام ليس في حالة توازن. سيشهد النظام لاحقًا رد فعل صافًا في اتجاه معدل أكبر ( تحول ) سيعود - إنشاء التوازن. تم تلخيص هذه الظاهرة من خلال مبدأ âلو شاتيلير’ إذا تم التأكيد على نظام التوازن ، فإن النظام سيشهد تحولًا في الاستجابة للإجهاد الذي يعيد إنشاء التوازن </م>. تتأثر معدلات التفاعل بشكل أساسي بالتركيزات ، كما هو موضح في قانون معدل التفاعل’ ودرجة الحرارة ، كما هو موضح في معادلة أرهينيوس. وبالتالي ، فإن التغيرات في التركيز ودرجة الحرارة هما عاملان من الضغوط التي يمكن أن تغير التوازن. تأثير التغيير في التركيز إذا تعرض نظام التوازن لتغير في تركيز مادة متفاعلة أو نوع منتج ، فإن معدل التفاعل الأمامي أو العكسي سيتغير. كمثال ، ضع في اعتبارك تفاعل التوازن: <img alt="Eq1" src="/files/ftp_upload/11391/11391_Equation 1v2.png" style="text-align: center; height: 48px;" /> عندما يكون هذا النظام في حالة توازن ، فإن معدلات التفاعل الأمامية والعكسية متساوية. <img alt="Eq2" src="/files/ftp_upload/11391/11391_Equation 2.png" style="text-align: center; height: 50px;" /> إذا تم الضغط على النظام بإضافة مادة متفاعلة ، إما N 2 أو O 2 ، فإن الزيادة الناتجة في التركيز تؤدي إلى زيادة معدل التفاعل الأمامي ، وتجاوز ذلك من رد الفعل العكسي: <img alt="Eq3" src="/files/ftp_upload/11391/11391_Equation 3.png" style="text-align: center; height: 50px;" /> سيختبر النظام صافي رد فعل مؤقت في الاتجاه الأمامي لإعادة التوازن ( سيتحول التوازن إلى اليمين ). سينتج هذا التحول نفسه في حالة إزالة بعض المنتجات NO من النظام ، مما يقلل من معدل رد الفعل العكسي ، مما يؤدي مرة أخرى إلى نفس عدم التوازن في المعدلات. يمكن استخدام نفس المنطق لشرح التحول إلى اليسار الناتج عن إزالة المادة المتفاعلة أو إضافة منتج إلى نظام التوازن. كل من هذه الضغوط تؤدي إلى زيادة معدل رد الفعل العكسي <img alt="Eq4" src="/files/ftp_upload/11391/11391_Equation 4.png" style="text-align: center; height: 50px;" /> وتفاعل صاف مؤقت في الاتجاه العكسي لإعادة التوازن. كبديل لهذا التفسير الحركي ، يمكن تبرير تأثير التغيرات في التركيز على التوازن من حيث حاصل التفاعل. عندما يكون النظام في حالة توازن ، <img alt="Eq5" src="/files/ftp_upload/11391/11391_Equation 5.png" style="text-align: center; height: 70px;" /> إذا تمت إضافة مادة متفاعلة (زيادة مقام حاصل التفاعل) أو تمت إزالة المنتج (إنقاص البسط) ، فعندئذٍ Qc & # 60 ؛ Kc وسوف يتحول التوازن إلى اليمين. لاحظ أن الطرق الثلاث المختلفة للحث على هذا الضغط تؤدي إلى ثلاثة تغييرات مختلفة في تكوين خليط التوازن. إذا تمت إضافة N 2 ، فإن التحول الصحيح سوف يستهلك O 2 وينتج NO عند إعادة التوازن ، مما ينتج عنه خليط بتركيز أكبر من N 2 و NO وتركيز أقل من O 2 مما كان موجودًا من قبل. إذا تمت إضافة O 2 ، فإن خليط التوازن الجديد سيكون له تركيزات أكبر من O 2 و NO وتركيز أقل من N 2 . أخيرًا ، إذا تمت إزالة NO ، فإن خليط التوازن الجديد سيكون له تركيزات أكبر من N 2 و O 2 وتركيز أقل من NO. على الرغم من هذه الاختلافات في التركيب ، ستكون قيمة ثابت التوازن هي نفسها بعد الضغط كما كانت من قبل (وفقًا لقانون الحركة الجماعية). يمكن تطبيق نفس المنطق على الضغوط التي تتضمن إزالة المواد المتفاعلة أو إضافة منتج ، وفي هذه الحالة Qc > Kc وسوف يتحول التوازن إلى اليسار. تم اقتباس هذا النص من <a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">Openstax, Chemistry 2e, Section 13.3 Shifting Equilibria: LeChatelier’s Principle</a>.

النظام في حالة توازن في حالة توازن ديناميكي ، مع حدوث تفاعلات أمامية وعكسية بمعدلات متساوية. إذا كان نظام التوازن ...

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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 reactant or product can move the equilibrium in one direction or the other.

Adding a reactant, such as N2 or O2 in the example reaction, increases the forward reaction rate. The forward rate then becomes greater than the reverse rate, so the equilibrium shifts right. Removing the product NO has the same effect because it lowers the reverse reaction rate and creates the same imbalance.

The opposite changes cause a left shift. Removing reactant or adding product increases the reverse reaction rate compared with the forward rate. The system then moves in the reverse direction until equilibrium is reached again.

This shift can also be explained with the reaction quotient, Qc, and the equilibrium constant, Kc. When reactant is added, Qc becomes less than Kc. When product is removed, Qc also becomes less than Kc, so the equilibrium shifts right. If reactant is removed or product is added, then Qc is greater than Kc and the equilibrium shifts left.

Although the final composition changes, the equilibrium constant stays the same after the stress is removed and the system rebalances. If N2 is added, the new mixture has more N2 and NO and less O2. If O2 is added, the mixture has more O2 and NO and less N2. If NO is removed, the mixture ends with more N2 and O2 and less NO. The same idea applies to shifts caused by removing reactant or adding product.

Shifting Equilibrium by Changing Concentration

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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...

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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

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...

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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)

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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

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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 changing concentration shifts chemical equilibrium, including why adding or removing reactants or products moves the reaction left or right.

Shifting Equilibrium by Changing Concentration | JoVE K12

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Shifting Equilibrium by Changing Concentration

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