Name: reaction order and rate constants
Uploaded: 2020-03-26T07:22:26.000Z
Duration: 4 min 37 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

3.2.1 9C.3.1.1.2

Concentration Dependence

يسمى مقياس سرعة استمرار التفاعل بمعدل التفاعل. بالنسبة للتفاعل أحادي الخطوة، يكون المعدل مساويا للتغير في تركيز كل مادة متفاعلة أو ناتج بمرور الوقت مضروبا في معكوس المعامل المتكافئ المقابل. يمكنك التفكير في التغير في التركيز بمرور الوقت على أنه التركيز في الوقت t ناقص تركيز البداية مقسوما على t. معدلات التفاعل دائما ما تكون موجبة ، لذا فإن تعبيرات المتفاعلة لها علامات سالبة. قد لا تكون هذه المعدلات متساوية في التفاعلات متعددة الخطوات، ولكن لا يزال بإمكاننا استخدام هذه العلاقة كتقدير للتفاعل الكلي. 
يصف قانون المعدل ، أو معادلة المعدل ، العلاقة بين سرعة التفاعل وتركيزات المادة المتفاعلة. في هذه المعادلة، k هو ثابت المعدل، A وB هما المتفاعلان، و m وn هما ترتيب تفاعل كل منهما. يصف ترتيب التفاعل العلاقة بين تركيز المادة المتفاعلة والمعدل ولا يرتبط بقياس التكافئ. من الضروري أن تتذكر أن ترتيب التفاعل يختلف عن معامل المادة المتفاعلة في المعادلة المتوازنة. 
عندما يتضمن التفاعل اثنين أو أكثر من المواد المتفاعلة، يجب أن نأخذ في الاعتبار ترتيب التفاعل لكل مادة متفاعلة. ترتيب التفاعل الكلي يساوي مجموع أوامر تفاعل المواد المتفاعلة. على سبيل المثال ، إذا كان المتفاعل A من الدرجة الأولى والمتفاعل B من الدرجة الصفرية ، فإن ترتيب التفاعل الكلي هو واحد. أوامر التفاعل الأكثر شيوعا في التفاعلات البسيطة هي الترتيب الصفري والدرجة الأولى والثانية. دعنا نتناولها باستخدام تفاعل أحادي الجزيء كمثال. 
إذا كان التفاعل صفرا ، فلن يكون لتركيز المادة المتفاعلة أي تأثير على معدل التفاعل. ومن ثم، فإن معدل التفاعل يساوي k، وهو ثابت المعدل. الرسم البياني لمعدل التفاعل بالنسبة للتركيز هو خط أفقي. 
في العلاقات من الدرجة الأولى ، يرتبط تركيز المادة المتفاعلة خطيا بمعدل التفاعل. وبالتالي ، فإن المعدل يساوي ثابت المعدل مضروبا في تركيز المادة المتفاعلة. سيكون الرسم البياني لمعدل التفاعل بالنسبة للتركيز خطيا ، مع k كمنحدر. 
إذا كان التفاعل من الدرجة الثانية ، فهناك علاقة تربيعية بين التركيز والمعدل. ومن ثم، فإن المعدل يساوي ثابت المعدل مضروبا في تربيع التركيز. سيكون الرسم البياني للمعدل بالنسبة للتركيز مكافئيا ، مع k كمنحدر. 
ثابت المعدل ، k ، هو قيمة تعتمد على درجة الحرارة تربط طاقة تنشيط التفاعل بمعدل التفاعل. سوف تستكشف هذا في التجربة المعملية التالية. 
عادة ما تعطى معدلات التفاعل بالمول لكل لتر في الثانية. المعدل له نفس الوحدات ، بغض النظر عن ترتيب التفاعل. وبالتالي ، فإن ثابت المعدل له وحدات مختلفة ، اعتمادا على ترتيب التفاعل. على سبيل المثال، إذا كان A هو الدرجة الأولى و B هو ترتيب صفر، فلدينا مثيل واحد من المولات لكل لتر في معادلة المعدل. لذلك ، يجب أن يكون ثابت المعدل بالثواني العكسية. 
إذن كيف نحدد ترتيب التفاعل؟ يجب تحديد ترتيب التفاعل تجريبيا باستخدام سلسلة من الاختبارات. إذا كان لديك مادتان متفاعلتان ، فإن إحدى الطرق هي الحفاظ على تركيز أحد المواد المتفاعلة ثابتا ، وتغيير الآخر ، والوقت الذي يستغرقه صنع كمية معينة من المنتج. تتكرر نفس العملية للمادة المتفاعلة الثانية. يمكنك بعد ذلك تقدير ترتيب كل مادة متفاعلة عن طريق رسم المعدل مقابل التركيز المتغير للمواد المتفاعلة ، ومعرفة ما إذا كان يبدو وكأنه رسم بياني من الدرجة الأولى أو الثانية. ستتيح لك مطابقة بياناتك مع معادلة المعدل المقابلة أيضا حساب k. 
في هذا المختبر ، ستحدد ترتيب تفاعل اثنين من المواد المتفاعلة عن طريق تغيير تركيزاتهما وتوقيت المدة التي يستغرقها التفاعل للتقدم إلى تحويل المحلول إلى معتم.

الاعتماد على التركيز

الحركية الكيميائية وقانون معدل التفاعل
تشير الحركية الكيميائية إلى معدل أو سرعة التفاعل الكيميائي. يعتمد المعدل على آلية التفاعل وتعقيده وعددها. يلعب تركيز المادة المتفاعلة أيضا دورا مهما في معدل التفاعل. 
يحدد قانون المعدل هذه العلاقة من خلال التجريب. يساهم كل مادة متفاعلة في سرعة التفاعل بعامل يعرف باسم ترتيب التفاعل. يمكن أن يتراوح هذا العامل من صفر إلى اثنين، ويعتمد على علاقة هذا المتفاعل بمعدل التفاعل. 
r = k[A]m[B]n ل aA + bB + ... → cC
في هذه المعادلة، r هو معدل التفاعل، k هو ثابت معدل التفاعل، [A] و[B] هما تركيزات المتفاعلتين A وB، وm وn هما رتبتا تفاعل المتفاعلتين A وB على التوالي. يتم تعريف معدل التفاعل ، r ، على أنه التغير في تركيز المنتج بمرور الوقت وله وحدات مول لكل لتر في الثانية. 
<h4>ترتيب رد الفعل</h4>
يصف ترتيب التفاعل اعتماد القدرة الذي يمتلكه تركيز المواد المتفاعلة على معدل التفاعل. ترتيب التفاعل الكلي هو مجموع أوامر التفاعل لكل مادة من المواد المتفاعلة. من المهم أن تتذكر أن ترتيب التفاعل هو NOT مرتبط بالعوامل المتكافئة للمعادلة الكيميائية المتوازنة. بمعنى آخر ، لا يمكن استخدام القياس المتكافئ لتحديد أوامر التفاعل للتفاعل الكيميائي. يجب تحديد أوامر التفاعل تجريبيا 
لتحديد ترتيب التفاعل ، يظل تركيز المادة المتفاعلة الثانية ثابتا ، بينما يختلف تركيز المادة المتفاعلة الأولى. يتم قياس الوقت الذي يستغرقه حدوث التفاعل بالثواني. ومع ذلك ، فإن هذه المرة لا تتوافق مع الوقت الذي يستغرقه التفاعل للانتقال إلى الانتهاء. بدلا من ذلك ، هذا هو الوقت الذي يستغرقه رد الفعل على start. ثم تتم مقارنة أوقات التفاعل لتركيزات المواد المتفاعلة المختلفة لتحديد الترتيب. يتم إجراء نفس سلسلة التفاعلات لتحديد ترتيب المادة المتفاعلة الثانية ، حيث يظل تركيز المتفاعل الأول ثابتا ويتنوع تركيز المتفاعل الثاني. 
من خلال مقارنة أوقات التفاعل ، يمكن تحديد ترتيب التفاعل. على سبيل المثال ، إذا ظل وقت التفاعل ثابتا على الرغم من التغييرات في تركيز المادة المتفاعلة ، فإن المادة المتفاعلة تكون صفرا. هذا يعني أن معدل التفاعل يساوي معامل معدل التفاعل، k، الذي يجب أن يحتوي على وحدات M/s. إذا تغير وقت التفاعل خطيا مع التغيرات في التركيز (أي أن مضاعفة التركيز يؤثر على وقت التفاعل بمعامل 2) ، فإن المادة المتفاعلة هي الدرجة الأولى. هذا يعني أن معدل التفاعل يساوي ناتج معامل معدل التفاعل وتركيز المادة المتفاعلة. في هذه الحالة ، يحتوي k على وحدات 1 / ثانية. أخيرا ، إذا تأثر زمن التفاعل بعامل 4 عندما يتضاعف تركيز المادة المتفاعلة ، فإن المادة المتفاعلة هي الدرجة الثانية. هذا يعني أن معدل التفاعل يساوي ثابت المعدل مضروبا في مربع تركيز المادة المتفاعلة، مكونا علاقة تربيعية. في هذه الحالة ، يجب أن تكون وحدات k 1 / M⋅s. 
الترتيب الكلي للتفاعل هو مجموع أوامر التفاعل الفردية. على سبيل المثال ، إذا كان التفاعل من الدرجة الأولى فيما يتعلق ب A ، فإن m = 1. وإذا كان التفاعل صفريا بالنسبة إلى B ، فإن n = 0. الترتيب الكلي للتفاعل هو من الدرجة الأولى لأن m + n = 1. 
<h4>ثابت معدل التفاعل</h4>
ثابت المعدل ، k ، خاص بالتفاعل ودرجة الحرارة التي يتم فيها تنفيذ التفاعل. يتم تحديد ثابت المعدل من سلسلة التجارب. باستخدام المعدل المقاس وتركيزات المادة المتفاعلة الأولية ، يتم استخدام معادلة المعدل لحل ثابت المعدل. يعتمد ثابت المعدل على درجة الحرارة ويتم تحديده بواسطة معادلة أرهينيوس. تصف هذه المعادلة العلاقة بين k وطاقة التنشيط، Ea، ودرجة الحرارة، T، وثابت الغاز المثالي، R. الثابت A هو ثابت التناسب ولا ينبغي الخلط بينه وبين المتفاعل A. 
<img src="/CDNSource/lm/labs/50/50_Concepts_2.jpg">
<h4>المراجع</h4>
<ol>
	<li style="font-size:17px">كوتز ، جي سي ، تريتشيل جونيور ، بي إم ، تاونسند ، جي آر (2012). الكيمياء والتفاعل الكيميائي. بلمونت ، كاليفورنيا: بروكس / كول ، Cengage Learning. </li>
	<li style="font-size:17px">سيلدربيرج ، MS (2009). الكيمياء: الطبيعة الجزيئية للمادة والتغيير. بوسطن ، ماساتشوستس: ماكجرو هيل. </li>
</ol>

الحركية الكيميائية وقانون معدل التفاعل
تشير الحركية الكيميائية إلى معدل أو سرعة التفاعل الكيميائي. يعتمد المعدل على الآلية ، ...

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JoVE Lab Manual

الكيمياء

reaction order and rate constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate.

In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is the rate constant, and [A] and [B] are the reactant concentrations. The exponents m and n show the reaction order for each reactant.

The reaction rate is the change in product concentration over time. Its units are moles per liter per second. The overall reaction order is the sum of the individual orders. Reaction order is not the same as the numbers in the balanced chemical equation, so stoichiometric coefficients cannot be used to find it. Reaction orders must be measured experimentally.

To find a reaction order, one reactant concentration is changed while the other is held constant. The reaction time is measured in seconds, but this is the time for the reaction to start, not the time to completion. The times from different concentrations are compared to determine the order. The same process is repeated for the second reactant by switching which concentration is varied.

If the reaction time stays the same even when concentration changes, the reactant is zero-order. In that case, the rate equals k, and k has units of M/s. If the time changes linearly with concentration, the reactant is first order. Then the rate equals k times the reactant concentration, and k has units of 1/s. If doubling the concentration changes the time by a factor of 4, the reactant is second order. Then the rate equals k times the square of the concentration, and k has units of 1/M·s.

The overall order is the sum of the individual orders. For example, if A is first order and B is zero-order, the total order is first order because m + n = 1. The rate constant, k, is specific to the reaction and the temperature used. It is found from the experimental data by using the measured rate and initial concentrations in the rate equation.

The rate constant also depends on temperature through the Arrhenius equation. This equation relates k to activation energy, Ea, temperature, T, and the ideal gas constant, R. The constant A in the equation is a proportionality constant. It should not be confused with reactant A.

Reaction Order and Rate Constants

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thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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Learn how concentration affects reaction rate, how to determine zero-, first-, and second-order reactions, and how rate constants depend on temperature.

Reaction Order and Rate Constants | JoVE K12

Alabama Course of Study Science

Matter and Its Interactions: Energy

9-12.C.3.3.d

Next Generation Science Standards

High School

Physical Science

Matter and Its Interactions

HS-PS1-5

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

استعد لتدريس الاعتماد على التركيز من خلال هذا الدليل الإرشادي للمدرسين لمدة 5 دقيقة. يغطي خطوات التحضير الأساسية لمختبر Chemistry على JoVE Lab Manual.

تحضير المدرّس لـ الاعتماد على التركيز في Chemistry - أكثر من 2.2K مشاهدة | JoVE Lab Manual

اتبع إجراءات الاعتماد على التركيز خطوة بخطوة في فيديو بروتوكول الطالب هذا لمدة 10 دقيقة. جزء من مجموعة Chemistry على JoVE Lab Manual.

بروتوكول الطالب لـ الاعتماد على التركيز في Chemistry - أكثر من 4.4K مشاهدة | JoVE Lab Manual

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes ...

Electron Behavior

Electrons are negatively charged subatomic particles that are attracted to an orbit around the positively-charged nucleus of an atom. They reside in ...

effect-of-temperature-change-on-reaction-rate

Effect of Temperature Change on Reaction Rate

The Arrhenius equation,

relates the activation energy and the rate constant, k, for many chemical reactions.
In this equation, R is the ideal gas ...

factors-influencing-the-rate-of-chemical-reactions

Factors Influencing the Rate of Chemical Reactions

A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the ...

Concentration and Rate Law

The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions ...

Measuring Reaction Rates

Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical ...

Temperature Dependence

Chemical Kinetics 
The reaction rate is the speed at which a chemical reaction occurs. The reaction rate is defined as the change in concentration of a ...

Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time ...

Chemical Kinetics and the Reaction Rate Law
Chemical kinetics refers to the rate or speed of a chemical reaction. The rate depends on the mechanism, ...

Matter and Its Interactions: Develop a model based on evidence to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. (P: 2, CC: 5, CI: PS1)

Solution Formation

There is no one solvent that can dissolve every type of solute. Some substances that readily dissolve in a certain solvent might be insoluble in a ...

Energetics of Solution Formation

The formation of a solution is an example of a spontaneous process, which is a process that occurs under specified conditions without energy from some ...

General Properties of Solutions

Many common substances around us exist as a solution, such as ocean water, air, and gasoline. All solutions are mixtures of substances that are composed ...

Solutions and Concentrations

Source: Laboratory of Dr. Michael Evans &#8212; Georgia Institute of Technology
A solution is a homogeneous mixture containing some components in small ...

Solubility

Solubility
Solubility describes how much of a solute can dissolve in a given volume of a specific solvent. Solubility is usually reported in terms of ...

Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture&#160;composed of a solvent, the major component, and a solute, the ...

Solution Equilibrium and Saturation

Imagine adding a small amount of sugar to a glass of water, stirring until all the sugar has dissolved, and then adding a bit more. You can repeat this ...

Intermolecular Forces in Solutions

The formation of a solution is an example of a spontaneous process, a process that occurs under specified conditions without energy from some external ...

Matter and Its Interactions: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. (P: 2, CC: 5, CI: PS1)

9C.3.1.1.3

Chemical and Solubility Equilibria

The free energy change associated with dissolving a solute in a liter of solvent is called the free energy of a solution, &#916;Gsolution. The overall ...

Matter and Its Interactions: Apply scientific principles and evidence to provide an explanation about the effects of changing the surface area, agitation, temperature, and concentration of the reacting particles on the rate at which the reaction occurs. (P: 6, CC: 1, CI: PS1)

9C.3.2.1.2

3 Developing possible explanations of phenomena or designing solutions to engineering problems
 3.2 Constructing explanations and designing solutions 
  3.2.1 Students will be able to apply scientific principles and empirical evidence (primary or secondary) to explain the causes of phenomena or identify weaknesses in explanations developed by the students or others.

Reaction Order and Rate Constants

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