Name: equilibrium concentrations from an ice table
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 5 s
Channel: JoVE

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.2

Calculating Equilibrium Concentrations

تركيزات التوازن المجهولة،يمكن تحديدها من خلال التركيزات الأولية للمواد المتفاعلة وثابت التوازن K،للتفاعل. لنتأمل التفاعل الذي فيه 0.30 مولار من غاز النيتروجين و 0.40 مولار من غاز الأكسجين،تتفاعل لتنتج غاز أكسيد النيتروجين وحيث تكون قيمة K 0.10. لحساب تركيزات التوازن،توج القيم المعروفة في جدول ICE.للتغيير في التركيز،زيادة أو نقصان كل من النواتج أو المواد المتفاعلة،على التوالي،يشار إليها بـX مضروبة في معاملات تكافؤ العناصر. يستخدم المجموع أو الفرق في إيجاد تركيزات التوازن،التي تُستبدل بعد ذلك داخل معادلة التوازن. إيجاد قيمة X،تُبسط المعادلة وتوضع جميع المعطيات في طرف واحد لتحويلها إلى الصيغة:مربع ax زائد bx زائد c.يمكن حل هذه المعادلة باستخدام الصيغة التربيعية. يُعطي الحل قيمتين لـX هما:0.047 and negative 0.065. بما أن التركيز السالب لمادة ما أمر مستحيل،يمكن رفض القيمة.باستخدام 0.047 لـ X،فإن تركيزات التوازن للنيتروجين والأكسجين،وأحادي أكسيد النيتروجين تساوي 0.25،و0.35،و0.094،على التوالي. حالة المربع الكامل هي أحد الأوضاع التي يُستخدم فيها اختصار لتجنب الصيغة التربيعية. على سبيل المثال،إذا كان التركيز الأولي للنيتروجين والأكسجين في التفاعل أعلاه كان 0.30 مولار لكل منهما،وهكذا تصبح المعادلة مربعًا كاملًا.في مثل هذه الحالات،يمكن تبسيط المعادلة بأخذ جذر المربع لطرفي المعادلة لإيجاد قيمة X.

<ol>
	<li>ليم ، كيران ف. "استخدام حاسبات الرسومات وجداول البيانات في الكيمياء: حل مشاكل التوازن". مجلة التربية الكيميائية 85 ، العدد 10 (2008): 1347. <a href = "https://pubs.acs.org/doi/pdf/10.1021/ed085p1347">https://pubs.acs.org/doi/pdf/10.1021/ed085p1347</a></li>
</ol>

حساب تركيزات التوازن

تعد القدرة على حساب تركيزات التوازن أمرًا ضروريًا للعديد من مجالات العلوم والتكنولوجيا— على سبيل المثال ، في صياغة وتحديد جرعات المنتجات الصيدلانية. بعد تناول الدواء أو حقنه ، فإنه يشترك عادة في عدة توازنات كيميائية تؤثر على تركيزه النهائي في نظام الجسم الذي يهمه الأمر. مطلوب معرفة الجوانب الكمية لهذه التوازنات لحساب كمية الجرعة التي ستلتمس التأثير العلاجي المطلوب. يمكن أن يكون النوع الأكثر صعوبة من حساب التوازن هو النوع الذي تُشتق فيه تركيزات التوازن من التركيزات الأولية وثابت التوازن. بالنسبة إلى هذه الحسابات ، يكون اتباع نهج من أربع خطوات مفيدًا عادةً: <ol><li> حدد الاتجاه الذي سيستمر فيه التفاعل للوصول إلى التوازن. </li><li> طور جدول ICE </li><li> احسب تغيرات التركيز ، وبالتالي ، تراكيز التوازن. </li><li> تأكيد تركيزات التوازن المحسوبة. </li></ol> حساب تركيزات التوازن في ظل ظروف معينة ، ثابت التوازنKc لتحلل PCl5(غ) إلى PCl3(غ) و Cl2(غ) يساوي 0.0211. يمكن استخدام الإجراء أعلاه لتحديد تركيزات التوازن لكل من Cl5, PCl3, و Cl2 في خليط يحتوي مبدئيًا على PCl فقط 5 بتركيز 1.00 M. الخطوة الأولى. تحديد اتجاه سير التفاعل. <img alt="Eq1" src="/files/ftp_upload/11390/11390_Equation 1.png" style="text-align: center; height: 50px;" /> نظرًا لوجود المادة المتفاعلة فقط في البداية ، Qc = 0 وسيبدأ التفاعل إلى اليمين. <tbody><tr><td style="color: black; border: 1px solid black; text-align: center;"></td><td style="color: black; border: 1px solid black; text-align: center;">     PCl5 (g)     </td><td style="color: black; border: 1px solid black; text-align: center;">  PCl3 (g)   </td><td style="color: black; border: 1px solid black; text-align: center;">  Cl2 (g)  </td></tr><tr><td style="color: black; border: 1px solid black; text-align: center;">Initial Concentration (M)</td><td style="color: black; border: 1px solid black; text-align: center;">1.00</td><td style="color: black; border: 1px solid black; text-align: center;">0</td><td style="color: black; border: 1px solid black; text-align: center;">0</td></tr><tr><td style="color: black; border: 1px solid black; text-align: center;">Change (M)</td><td style="color: black; border: 1px solid black; text-align: center;">−x</td><td style="color: black; border: 1px solid black; text-align: center;">+x</td><td style="color: black; border: 1px solid black; text-align: center;">+x</td></tr><tr><td style="color: black; border: 1px solid black; text-align: center;">Equilibrium Concentration (M)</td><td style="color: black; border: 1px solid black; text-align: center;">1.00 − x</td><td style="color: black; border: 1px solid black; text-align: center;">x</td><td style="color: black; border: 1px solid black; text-align: center;">x</td></tr></tbody></table>
 
 الخطوة 3. حل من أجل التغيير وتركيزات التوازن. ينتج عن استبدال تركيزات التوازن في معادلة ثابت التوازن <img alt="Eq2" src="/files/ftp_upload/11390/11390_Equation 2.png" style="text-align: center; height: 170px;" /> يمكن إعادة ترتيب معادلة ax2 + bx + c = 0 بالصيغة التالية لحلها من أجل x: <img alt="Eq3" src="/files/ftp_upload/11390/11390_Equation 3.png" style="text-align: center; height: 90px;" /> في هذه الحالة، a = 1, b = 0.0211, و c = −0.0211. ينتج عن استبدال القيم المناسبة لـ a, b, و c التالي:<img alt="Eq4" src="/files/ftp_upload/11390/11390_Equation 4.png" style="text-align: center; height: 90px;" /> إن جذور المعادلة التربيعية هما، بالتالي، <img alt="Eq5" src="/files/ftp_upload/11390/11390_Equation 5.png" style="text-align: center; height: 50px;" /> بالنسبة لهذا السيناريو، يكون الجذر الموجب فقط هو الذي له معنى ماديًا (تكون التركيزات إما صفرية أو موجبة) ، وبالتالي فإنx = 0.135 M. تركيزات التوازن هي <img alt="Eq6" src="/files/ftp_upload/11390/11390_Equation 6.png" style="text-align: center; height: 130px;" />< الخطوة 4. تأكيد تركيزات التوازن المحسوبة. يؤدي الاستبدال في تعبير Kc (للتحقق من عملية الحساب) إلى <img alt="Eq7" src="/files/ftp_upload/11390/11390_Equation 7.png" style="text-align: center; height: 90px;" /> ثابت التوازن المحسوب من تركيزات التوازن يساوي قيمة K c المعطاة في المسألة (عند تقريبه إلى العدد المناسب للأرقام المعنوية). < / ص>تم اقتباس هذا النص من <a href="https://openstax.org/books/chemistry-2e/pages/13-4-equilibrium-calculations">Openstax, Chemistry 2e, Section 13.4 Equilibrium Calculations</a><a href="https://openstax.org/books/chemistry-2e/pages/13-4-equilibrium-calculations">.</a>

تعد القدرة على حساب تركيزات التوازن أمرا ضروريا للعديد من مجالات العلوم والتكنولوجيا - على سبيل المثال ، في الصياغة والجرعات ...

Education

JoVE Core

الكيمياء

واحد

Chemical Equilibrium

الاتزان الكيميائي

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 effect.

A common approach is needed when equilibrium concentrations must be derived from starting values and a known Kc. The first step is to decide which way the reaction will move to reach equilibrium. Next, an ICE table is set up. ICE stands for initial, change, and equilibrium. After that, the concentration changes are solved and used to find the equilibrium concentrations. The final step is to check the answer.

The decomposition of PCl5(g) into PCl3(g) and Cl2(g) shows how this works. In the example, Kc is 0.0211, and the mixture starts with only PCl5 at 1.00 M. Because only the reactant is present at the start, Qc equals 0, so the reaction moves to the right. The ICE table gives an initial concentration of 1.00 M for PCl5 and 0 for the products, with changes of -x, +x, and +x.

Substituting the equilibrium values into the Kc expression leads to a quadratic equation. Solving it gives two roots, but only the positive root is physically meaningful because concentrations cannot be negative. In this case, x = 0.135 M. The equilibrium concentrations are then found for PCl5, PCl3, and Cl2. A final substitution into the Kc expression confirms that the calculated value matches the given equilibrium constant when rounded correctly.

Equilibrium Concentrations from an ICE Table

equilibrium-concentrations-from-an-ice-table

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

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 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 to find equilibrium concentrations with an ICE table, use Kc, and check answers with a PCl5 decomposition example for high school chemistry.

Equilibrium Concentrations from an ICE Table | JoVE K12

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Physical Science

Chemical Reactions

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Equilibrium Concentrations from an ICE Table

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