Name: stoichiometry, rates, and equilibrium
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 26 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.8

IPC.8.A

Chemical Reactions

ضع في اعتبارك تفاعلا كيميائيا متوازنا ، مثل احتراق غاز الهيدروجين. هنا ، العلاقة الكمية بين المواد المتفاعلة والنواتج - H2 و O2 و H2O - هي أن جزيئين من H2 يتفاعلان مع جزيء واحد من O2 لإنتاج جزيئين من H2O. تعرف هذه العلاقة الكمية باسم القياس المتكافئ.
في التفاعل الكيميائي ، تتفاعل المواد المتفاعلة مع بعضها البعض لتكوين المنتجات. المادة المتفاعلة المستهلكة بالكامل هي المادة المتفاعلة المحددة، والمادة المتفاعلة الموجودة بكمية أكبر من اللازم للتفاعل تماما مع المادة المتفاعلة المحددة هي المادة المتفاعلة الزائدة.
يتضمن التفاعل الكيميائي التحول الكيميائي للمواد المتفاعلة إلى منتجات. مع تقدم التفاعل ، ينخفض تركيز المواد المتفاعلة بينما يزداد تركيز المنتجات. يمكن رسم هذا التباين في تركيزات المواد المتفاعلة والمنتجات في رسم بياني كدالة للوقت.
تسمى السرعة التي يتقدم بها التفاعل معدل التفاعل. يقيس معدل اختفاء المواد المتفاعلة أو معدل ظهور المنتجات ويتم التعبير عنه بوحدات المولارية في الثانية.
التفاعل الكيميائي القابل للانعكاس هو التفاعل الذي يحدث فيه تحويل المواد المتفاعلة إلى منتجات وتحويل المنتجات مرة أخرى إلى مواد متفاعلة في وقت واحد. يشير السهم المزدوج بين المواد المتفاعلة والمنتجات إلى طبيعتها القابلة للانعكاس.
عندما يساوي معدل تكوين المنتجات ، أو معدل التفاعل الأمامي ، معدل تكوين المواد المتفاعلة ، أو معدل التفاعل العكسي ، يتحقق التوازن الكيميائي.
يكتب التعبير الثابت عن الاتزان على أنه التركيزات المولية للناتجين ، C و D ، فوق المتفاعلات ، A و B ، عند الاتزان ، كل منهما مرتفع إلى المعاملات المتكافئة الخاصة بها. عند حلها، يكون التعبير مساويا لثابت التوازن، Kc.
يمكن أيضا كتابة تعبير بنفس الشكل للمواد المتفاعلة والمنتجات بأي تركيز ، وتعرف الكمية المحسوبة باسم حاصل التفاعل ، Qc.

التفاعلات الكيميائية

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توفر المعادلة الكيميائية المتوازنة معلومات عن الصيغ الكيميائية للمواد المتفاعلة والمواد الناتجة المشاركة في التغير الكيميائي. تساعد قياسة تفاعل معين على التنبؤ بكمية المادة المتفاعلة اللازمة لإنتاج الكمية المطلوبة من المادة الناتجة، أو في بعض الحالات، كمية المادة الناتجة التي سيتم تشكيلها من كمية محددة من المادة المتفاعلة. 
غالبًا ما يشار إلى الكميات النسبية للمواد المتفاعلة والمواد الناتجة الممثلة في معادلة كيميائية متوازنة بالكميات المتكافئة. ومع ذلك، في الواقع، لا تكون المواد المتفاعلة موجودة دائمًا بالكميات المتكافئة التي تشير إليها المعادلة المتوازنة. 
في التفاعل الكيميائي، المادة المتفاعلة التي يتم استهلاكها أولاً، والتي تحدد كمية المادة الناتجة المتكونة، هي المادة المتفاعلة المحددة، بينما تصبح المادة الأخرى هي المادة المتفاعلة الزائدة. غالبًا ما يتم استخدام فائض من مادة متفاعلة واحدة أو أكثر لضمان التحويل الكامل للمادة المتفاعلة الأخرى إلى المنتج.
 النظر في تفاعل تكوين الماء الممثل بالمعادلة: 
<img alt="Eq1" src="/files/ftp_upload/11691/11691_Equation1.svg" style="text-align: center; height: 20px;"> 
يشير قياس العناصر الكيميائية إلى أن مولين من الهيدروجين ومول واحد من الأكسجين يتفاعلان لإنتاج مولين من الماء؛ أي أن الهيدروجين والأكسجين يتحدان بنسبة 2:1.
 تخيل لو كان هناك 5 مولات من الهيدروجين و 2 مول من الأكسجين. أصبحت نسبة المواد المتفاعلة الآن 5:2 (أو 2.5:1)، وهي أكبر من النسبة المتكافئة البالغة 2:1. وبالتالي فإن الهيدروجين موجود بكميات زائدة، والأكسجين هو المادة المتفاعلة المحددة. تفاعل كل الأكسجين المقدم (2 مول) سوف يستهلك 4 مول من 5 مول من الهيدروجين المقدم، ويترك 1 مول من الهيدروجين دون تفاعل. يعد حساب الكميات المولية لكل مادة متفاعلة ومقارنتها بالكميات المتكافئة الممثلة في المعادلة الكيميائية المتوازنة إحدى طرق تحديد المواد المتفاعلة المحددة والزائدة. سرعة التفاعل هو التغير في كمية المادة المتفاعلة أو المنتجة في وحدة الزمن. ولذلك يتم تحديد معدلات السرعة عن طريق قياس الاعتماد الزمني لبعض الخصائص التي يمكن أن تكون مرتبطة بكميات المواد المتفاعلة أو المواد المنتجة.
 <img alt="Figure1" src="/files/ftp_upload/11691/11691_Figure1.png" style="text-align: center; height: 300px;"> 
يمكن رسم سرعة التفاعل الكيميائي في رسم بياني على أنه التباين في تركيزات المواد المتفاعلة والمنتجات كدالة للزمن. 
يمثل التفاعل الكيميائي العكسي عملية كيميائية تتم في الاتجاهين الأمامي (من اليسار إلى اليمين) والعكس (من اليمين إلى اليسار). يتم تقييم حالة التفاعل العكسي بشكل ملائم من خلال تقييم حاصل التفاعل (Q). للحصول على تفاعل عكسي وصفه <img alt="Eq2" src="/files/ftp_upload/11691/11691_Equation2.svg" style="text-align: center; height: 20px;"> يتم اشتقاق حاصل التفاعل مباشرة من قياس العناصر الكيميائية للمعادلة المتوازنة <img alt="Eq3" src="/files/ftp_upload/11691/11691_Equation3.svg" style="text-align: center; height: 44px;"> 
حيث يشير الحرف c إلى استخدام التركيزات المولية في التعبير. 
<img alt="Figure2" src="/files/ftp_upload/11691/11691_Figure2.png" style="text-align: center; height: 300px;"> عندما تكون معدلات السرعةات الأمامية والعكسية متساوية، تظل تركيزات أنواع المواد المتفاعلة والناتجة ثابتة مع مرور الوقت ويكون النظام في حالة توازن. يتم استخدام سهم مزدوج خاص للتأكيد على الطبيعة العكسية للتفاعل.
هذه المقالة مقتبسة من <a href="https://openstax.org/books/chemistry-2e/pages/4-3-reaction-stoichiometry">OpenStax Chemistry 2e, Section 4.3: Reaction Stoichiometry</a>; <a href="https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields">Section 4.4: Reaction Yield</a>; <a href="https://openstax.org/books/chemistry-2e/pages/12-1-chemical-reaction-rates#12163">Section 12.1: Chemical Reaction Rates</a>; <a href="https://openstax.org/books/chemistry-2e/pages/13-1-chemical-equilibria">Section 13.1 Chemical Equilibria</a>, <a href="https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants">Section 13.2 Equilibrium Constants</a><a href="https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants">.</a>
 </div>

توفر المعادلة الكيميائية المتوازنة معلومات الصيغ الكيميائية للمواد المتفاعلة والمنتجات المشاركة في التغير الكيميائي. A ...

Education

JoVE Core

Organic Chemistry

الكيمياء العضوية

Unit 1

الوحدة الأولى

Thermodynamics and Chemical Kinetics

الديناميكا الحرارية والحركية الكيميائية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

stoichiometry, rates, and equilibrium

Stoichiometry, reaction rates, and equilibrium explain how chemical reactions are measured and predicted. A balanced chemical equation shows the chemical formulas of the reactants and products in a chemical change. It also gives the relative amounts of each substance involved.

Reaction stoichiometry helps predict how much reactant is needed to make a desired amount of product. It can also show how much product forms from a given amount of reactant. The amounts shown by a balanced equation are called stoichiometric amounts.

In real reactions, reactants are not always present in the exact amounts shown by the equation. The limiting reactant is the substance that gets used up first. It limits how much product can form. The other substance is the excess reactant. Extra reactant is often added so the other reactant can be fully converted into product.

Water formation is a clear example. The balanced equation shows that 2 moles of hydrogen react with 1 mole of oxygen to make 2 moles of water. This is a 2:1 ratio. If 5 moles of hydrogen and 2 moles of oxygen are available, the ratio is 5:2, or 2.5:1. Hydrogen is then in excess, and oxygen is the limiting reactant. All 2 moles of oxygen use 4 moles of hydrogen, leaving 1 mole of hydrogen unreacted.

Reaction rate is the change in the amount of a reactant or product per unit time. Scientists find reaction rates by measuring how a property changes over time if that property can be linked to reactant or product amounts. A rate graph can show how reactant and product concentrations vary with time.

Some reactions are reversible, which means they can proceed in both the forward and reverse directions. The reaction quotient, Q, helps assess the status of a reversible reaction. It is based on the stoichiometry of the balanced equation, and the subscript c shows that molar concentrations are used in the expression. When the forward and reverse rates are equal, concentrations stay constant and the system is at equilibrium. A double arrow is used to show that the reaction is reversible.

Stoichiometry, Rates, and Equilibrium

chemical reactions

Stoichiometry, reaction rates, and equilibrium explain how chemical reactions are measured and predicted. A balanced chemical equation shows the chemical formulas of the reactants and products in a chemical change. It also gives the relative amounts of each substance involved. Reaction stoichiometry helps predict how much reactant is needed to make a desired amount of product. It can also show how much product forms from a given amount of reactant. The amounts shown by a balanced equation are...

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Combustion Heat and Hydrocarbon Stability

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Why Some Solutions Form Spontaneously

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entropy and solvation

Hydrophobic Effects in Solvation

Solvation is the process of surrounding a solute with solvent. It spreads the solute evenly through the solvent. A useful rule is that like dissolves like. A good solvent has molecular features similar to the substance being dissolved. Polar solvents dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent has a high dielectric constant, with ε greater than or equal to 15. An apolar solvent has a low dielectric constant. The dielectric constant is defined by the...

gibbs free energy and thermodynamic favorability

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Temperature Effects on Gibbs Free Energy

Temperature changes can decide whether a process is spontaneous. This idea applies to phase changes and to some chemical reactions. The key link is Gibbs free energy, which connects free energy change with enthalpy and entropy. The sign of the Gibbs free energy change, or ΔG, depends on the signs of enthalpy change (ΔH) and entropy change (ΔS), and sometimes on the absolute temperature. Because temperature is measured in kelvin, it is always a positive value. That means there are four main...

chemical and solubility equilibria

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Solubility depends on free energy changes when a solute dissolves in a solvent. The free energy change for this process is called the free energy of solution, ΔGsolution. When ΔGsolution is less than zero, solution formation is favorable. When it is greater than zero, solution formation is unfavorable. For complete dissolution to happen, the Gibbs energy change must be negative. This means the balance of forces in the mixture must favor solution formation. The amount a solute dissolves in a...

rate law and reaction order

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Reaction rate depends on reactant concentration, and rate laws show that relationship with a mathematical equation. A rate law, also called a differential rate law or rate equation, links the rate of a chemical reaction to the concentrations of its reactants. For a generic reaction, a A + b B  products, the rate law can be written as rate = k [A]^m [B]^n. Here, [A] and [B] are the molar concentrations of the reactants. The constant k is the rate constant, and it is specific to one reaction at...

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Arrhenius Equation in Reaction Speed

The Arrhenius equation connects activation energy, temperature, and the rate constant, k, for many chemical reactions. It helps explain why some reactions move slowly while others happen faster. In this equation, R is the ideal gas constant, with a value of 8.314 J/mol·K. T is the temperature in kelvin, Ea is the activation energy in joules per mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor, A, describes how often reacting molecules collide and how well...

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Chemical reactions can happen in a sequence of steps. A balanced chemical equation shows the reactants and products, but it does not show how the reaction occurs at the molecular level. The reaction mechanism, or reaction path, gives that step-by-step detail. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and together they add up to the balanced equation for the overall reaction. In a multistep mechanism, one step is often much slower than the...

bond dissociation energy and activation energy

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How Bond Strength Shapes Reaction Speed

Bond strength and activation energy help explain why organic reactions happen. Bond energy is the energy needed to break a bond homolytically, which means each atom takes one of the shared electrons. When a bond value is given for one specific bond, it is called bond dissociation energy. When it is given for a bond type across many compounds, it is called average bond energy. Bond dissociation energy usually follows a clear pattern. A single bond is weaker than a double bond, and a double bond...

energy diagrams, transition states, and intermediates

energy-diagrams-transition-states-and-intermediates

Reaction Coordinate Diagrams in Chemical Reactions

Reaction coordinate diagrams show how energy changes during a chemical reaction. These free-energy graphs use the horizontal axis to show reaction progress. Points near the reactants look like the reactants, while points near the products look like the products. The peaks on the diagram represent stable structures with measurable lifetimes. Other points on the curve are unstable and cannot be isolated. The high-energy, unstable peak is called the transition state, or activated complex. At the...

predicting reaction outcomes

How Temperature Changes Reaction Rate

Reaction rate and reaction pathway are key ideas in chemical kinetics. Thermodynamics, by contrast, focuses on the state of a system. It describes the properties, behavior, and components of reactants and products. It does not describe the path of the process or the speed of the reaction. Kinetics gives information on the atomic or molecular level, while thermodynamics focuses on the energetics of the reactants and products. Thermodynamics can show what may happen in a reaction, but it does...

key terms and concepts

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IPC.8.B

Louisiana Student Standards for Science

Chemistry

Matter And Its Interactions

HS-PS1-6

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.3

CHEM1.PS1.4

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.f

Florida Department of Education

Physical Science

SC.912.P.10

SC.912.P.10.6

SC.912.P.10.12

SC.912.P.12

SC.912.P.12.12

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS1-6

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Oxidation-Reduction Reactions

Oxidation&ndash;Reduction Reactions

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Oxidation Numbers

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Acids, Bases and Neutralization Reactions

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combustion-energy-a-measure-of-stability-in-alkanes-and-cycloalkanes

Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes

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Investigate how changes in properties are indicative of chemical reactions such as hydrochloric acid with a metal, oxidation of metal, combustion, and neutralizing an acid with a base.

Balancing Redox Equations

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chemical-equilibria-redefining-equilibrium-constant

Chemical Equilibria: Redefining Equilibrium Constant

Recall that the solubility of a sparingly soluble salt increases with the addition of an inert salt in a phenomenon known as the salt effect.
The extent ...

Factors Affecting Activity Coefficient

The activity coefficient of an ion depends on the ionic strength of the solution.
As indicated by the Debye&#8211;H&#252;ckel theory, when the ionic ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Develop and use models to balance chemical equations and support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Nuclear Fission

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Nuclear Power

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Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

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Biological Effects of Radiation

All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break ...

Research and communicate the uses, advantages, and disadvantages of nuclear reactions in current technologies.

IPC.8.C

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

Global Climate Change

Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global ...

Climate Change

The certainty of climate change remains a public controversy despite the consensus among approximately 97% of active climate researchers, who not only ...

Sustainable Development

As the human population continues to grow and use resources, we must be mindful of our planet&rsquo;s natural limits. Sustainable development provides a ...

Construct and communicate an evidence-based explanation of the environmental impact of the end-products of chemical reactions such as those that may result in degradation of water, soil, air quality, and global climate change.

IPC.8.D

Science concepts. The student knows that changes in matter affect everyday life. The student is expected to:

Stoichiometry, Rates, and Equilibrium

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