Name: reaction order from concentration
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 3 min 3 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.F

Concentration and Rate Law

يعتمد معدل التفاعل غالبًا،على تركيز المواد المتفاعلة. في أي تفاعل،قد يُعبّر عن العلاقة بين معدل التفاعل وتركيز المواد المتفاعلة رياضيًا باستخدام قانون معدلات أو معادلة. في قانون سرعة مثلًا،تمثل ثابت التوزيع النسبي،أو ثابت السرعة،وتمثل درجة التفاعل بالنسبة لمادة متفاعلة واحدة،تكون قيمتها غالبًا عددًا صحيحًا.في قوانين السرعة الخاصة بالتفاعلات متعددة المكونات،تكون درجة التفاعل الإجمالية،مساوية لدرجات جميع المواد المتفاعلة. لكل مادة متفاعلة،فإن معدل التفاعل،وثابت السرعة،والتركيز،ودرجة التفاعل تحدد جميعًا بالتجربة. يعبر قانون السرعة عن العلاقة بين جميع هذه القياسات.درجات المواد المتفاعلة الفردية،تأخذ،عادة،قيم 0،1،أو 2 واعتمادًا على درجة التفاعل الكلي،يمكن تصنيف التفاعلات الكيميائية إلى،تفاعلات درجة صفرية،ودرجة أولى،ودرجة ثانية. في تفاعل كيميائي أحادي-المتفاعل،او احادي الجزئ،والذي تبقى فيه معدلات التفاعل ثابتة طول مدة التفاعل،يكون تفاعلًا صفري الدرجة. درجة المادة المتفاعلة في تفاعل صفري تكون صفرًا،وبناء على قانون معدلات السرعة،يُرفع تركيز المادة المتفاعلة إلى القوة صفر.وبما أن قيمة أي عدد مرفوع للقوة صفر تساوي واحد،يكون معدل التفاعل لتفاعل من الدرجة الصفرية مساويًا لثابت المعدل،وبالتالي،لا يعتمد على تركيز المادة المتفاعلة. لذلك ففي تفاعل من الدرجة الصفرية،حتى عندما يتناقص تركيز المواد المتفاعلة،فإن معدل سرعة التفاعل لا يتباطأ. التفاعل الكيميائي أحادي الجزيء حيث معدل سرعة التفاعل يتناسب طرديًا،مع تركيز المادة المتفاعلة هو تفاعل من الدرجة الأولى.تكون درجة المادة المتفاعلة في تفاعل من الدرجة الأولى،واحد،ووفقًا لقانون معدل السرعة،يُرفع تركيز المادة المتفاعلة إلى القوة واحد. وبما أن قيمة أي عدد مرفوع للقوة واحد لا تتغير،يكون اعتماد معدل التفاعل في تفاعل من الدرجة الأولى معتمدًا بشكل مباشر على تركيز المادة المتفاعلة. ومع تناقص تركيز المادة المتفاعلة،يتناقص معدل سرعة التفاعل بنسبة مماثلة بصورة خطية.التفاعل الكيميائي أحادي الجزيء،الذي يعتمد معدل سرعة تفاعله على مربع تركيز المادة المتفاعلة،هو تفاعل من الدرجة الثانية. درجة المادة المتفاعلة هي اثنان،ويُرفع تركيز المادة المتفاعلة إلى القوة اثنين. وبناء عليه،فإن معدل سرعة التفاعل في تفاعل من الدرجة الثانية يعتمد بشكل مباشر على مربع قيمة تركيز المادة المتفاعلة.وبتناقص تركيز المادة المتفاعلة،يتناقص معدل سرعة التفاعل زيادة أسّية بمعدل تربيعي.

قانون التركيز والمعدّل

يتأثر معدل التفاعل بتركيزات المواد المتفاعلة. قوانين المعدل (قوانين المعدل التفاضلي) أو معادلات المعدل هي تعبيرات رياضية تصف العلاقة بين معدل التفاعل الكيميائي وتركيز المواد المتفاعلة. على سبيل المثال ، في تفاعل عام aA + bB ⟶ المنتجات ، حيث تكونa and b معاملات متكافئة ، يمكن كتابة قانون المعدل على النحو التالي:  <img alt="Eq1" src="/files/ftp_upload/11375/11375_Equation_1.png" style="height: 50px;" /> [A] و [B] يمثلان التركيزات المولية للمواد المتفاعلة ، و k هو ثابت المعدل ، وهو خاص بتفاعل معين عند درجة حرارة معينة. الأُسّان m و n عبارة عن أوامر رد فعل وعادة ما تكون أعدادًا صحيحة موجبة ، على الرغم من أنها يمكن أن تكون كسورًا أو سالبة أو صفرًا. يتم تحديد ثابت المعدل k وأوامر التفاعل m و n بشكل تجريبي من خلال ملاحظة كيفية تغير معدل التفاعل كتركيزات من المتفاعلات تغيرت. ثابت المعدل k مستقل عن تراكيز المادة المتفاعلة ، لكنه يختلف باختلاف درجة الحرارة. تصف أوامر التفاعل في قانون المعدل الاعتماد الرياضي للمعدل على تركيزات المادة المتفاعلة. الإشارة إلى قانون المعدل العام (المعدل = k[A]m[B]n)، يكون التفاعل m ترتيبًا بالنسبة إلى A و n ترتيب بالنسبة إلى B. على سبيل المثال، إذا كان m = 1 و n = 2، يكون التفاعل من المرتبة الأولى في الترتيب A والثاني في B. الترتيب العام للتفاعل هو ببساطة مجموع أوامر كل متفاعل. بالنسبة لمثال قانون المعدل هنا ، يكون التفاعل من الدرجة الثالثة بشكل عام (1 + 2 = 3). تتمثل إحدى الطرق التجريبية الشائعة لتحديد قوانين المعدل في طريقة المعدلات الأولية. تتضمن هذه الطريقة قياس معدلات التفاعل لتجارب تجريبية متعددة أجريت باستخدام تركيزات مختلفة من المتفاعلات الأولية. تسمح مقارنة المعدلات المقاسة لهذه التجارب بتحديد أوامر التفاعل ، وبالتالي ، ثابت المعدل ، اللذين يتم استخدامهما معًا لصياغة قانون معدل. قد تعرض قوانين المعدل أوامر جزئية لبعض المواد المتفاعلة ، وأحيانًا يتم ملاحظة أوامر التفاعل السلبية عندما تؤدي الزيادة في تركيز أحد المتفاعلات إلى انخفاض معدل التفاعل. من المهم ملاحظة أن قوانين المعدل يتم تحديدها عن طريق التجربة فقط ولا يتم التنبؤ بها بشكل موثوق من خلال قياس العناصر المتفاعلة. يحدد ترتيب التفاعل العلاقة بين معدل التفاعل وتركيز المواد المتفاعلة أو المنتجات. • في تفاعل صفري الترتيب، لا يكون لتركيز المواد المتفاعلة أي تأثير على معدل التفاعل ، الذي يظل ثابتًا طوال الوقت. • في تفاعل من الدرجة الأولى ، يتناسب معدل التفاعل بشكل مباشر وخطي مع التغير في تركيز المادة المتفاعلة. مع انخفاض تركيز المادة المتفاعلة ، ينخفض ​​معدل التفاعل أيضًا بشكل متناسب. • في التفاعلات من الدرجة الثانية أو الأعلى ، يتناسب معدل التفاعل مع القيمة الأسية للمتفاعلات. لذلك ، مع تقدم التفاعل وانخفاض تركيز المواد المتفاعلة ، ينخفض ​​معدل التفاعل بشكل كبير. هذا النص مقتبس من <a href="https://openstax.org/books/chemistry-2e/pages/12-3-rate-laws#57033">Openstax, Chemistry 2e, Section 12.3: Rate Laws</a>.

يتأثر معدل التفاعل بتركيزات المواد المتفاعلة. قوانين المعدل (قوانين المعدل التفاضلي) أو معادلات المعدل هي تعبيرات رياضية ...

Education

JoVE Core

Chemistry

الكيمياء

واحد

Chemical Kinetics

الحركية الكيميائية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

reaction order from concentration

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k.

In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n are the reaction orders. They are usually positive integers, but they can also be fractions, negative numbers, or zero. The values of k, m, and n are found experimentally by measuring how the rate changes when reactant concentrations change.

The rate constant does not depend on the reactant concentrations, but it can change with temperature. The reaction orders show the mathematical link between concentration and rate. In the expression rate = k [A]m [B]n, the reaction is m order with respect to A and n order with respect to B. For example, if m = 1 and n = 2, the reaction is first order in A and second order in B.

The overall reaction order is the sum of the orders for each reactant. In the example above, the reaction is third order overall because 1 + 2 = 3. A common way to find a rate law is the method of initial rates. In this method, reaction rates are measured in several trials that start with different initial reactant concentrations. Comparing those rates makes it possible to find the reaction orders and then the rate constant.

Rate laws can also include fractional orders. In some cases, a reactant may have a negative order. That means increasing its concentration can lower the reaction rate. Rate laws are determined by experiment only, and they cannot be reliably predicted from reaction stoichiometry. The reaction order also describes how the rate changes as reactant or product concentration changes.

A zero-order reaction has a rate that does not change with reactant concentration. The rate stays constant throughout the reaction. In a first-order reaction, the rate is directly proportional to the change in reactant concentration. As the reactant concentration drops, the rate drops by the same proportion. In second-order or higher-order reactions, the rate depends on the reactants raised to an exponent. As the reaction continues and reactant concentration decreases, the rate falls exponentially.

Reaction Order from Concentration

reaction rate

Measuring Reaction Rates

Measuring reaction rates shows how fast reactants are used up or products are formed over time. The rate of reaction is the change in the amount of a reactant or product per unit time. Because of that, scientists measure how a property changes as the reaction proceeds and connect that change to reactant or product amounts. For reactions that make or use a gas, the rate can be followed by changes in volume or pressure. A rate expression is the mathematical way to write how concentration changes...

measuring reaction rates

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Reaction kinetics can be tracked with polarimetry, spectrometry, and pressure measurements. These methods let scientists follow a reaction without disturbing the sample. They also help determine how reactant or product concentrations change over time. Polarimetry is used for optically active substances. These substances rotate the plane of polarized light, which is called optical rotation. The effect comes from molecular structure. Normal monochromatic light is unpolarized, but after it passes...

concentration and rate law

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k. In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n...

determining order of reaction

Finding Rate Law from Initial Rates

Rate laws connect the speed of a chemical reaction to the concentration of its reactants. The rate constant, k, and the reaction orders are not taken from the chemical equation. They are found experimentally by watching how the rate changes when the reactant concentrations change. One common way to do this is the method of initial rates. In this method, several trials are run with different starting concentrations. The measured rates are then compared to determine the reaction orders and,...

the integrated rate law: the dependence of concentration on time

the-integrated-rate-law-the-dependence-of-concentration-on-time

Reading Reaction Progress with Integrated Laws

Integrated rate laws connect reaction concentration to time. They help show how much reactant or product is present after a certain period. They can also help estimate how long a reaction must run to reach a given extent. A common use is finding how long radioactive material must be stored before its radioactivity drops to a safe level. These equations come from the differential rate law after it is integrated with respect to time. For a first-order reaction, where rate = k[A], the integrated...

half-life of a reaction

Reaction Half-Life in Kinetics

Reaction half-life is the time needed for half of a reactant to be consumed. After each half-life, half of the remaining reactant is used up. A hydrogen peroxide decomposition example shows this pattern clearly. The concentration drops from 1.000 M to 0.500 M in the first 6.00 hours, then to 0.250 M in the next 6.00 hours, and then to 0.125 M in the third period. Each later 6.00-hour interval removes half of what is left. For first-order reactions, the half-life does not depend on the reactant...

temperature dependence on reaction rate

Collision Theory and Reaction Speed

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arrhenius plots

Determining Activation Energy from Temperature

The Arrhenius equation links activation energy and the rate constant, k, for chemical reactions. It is written as k = Ae−Ea/RT. In this equation, R is the ideal gas constant with a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor depends on collision frequency and the orientation of reacting molecules. Experimental kinetic data can be used to find the activation...

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Chemical reactions can happen in steps, and a balanced equation does not show the full path at the molecular level. A reaction mechanism, also called a reaction path, gives the step-by-step process that explains how reactants become products. The decomposition of ozone is one example of a reaction that can be described by a sequence of steps. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and when they are added together, they give the balanced...

rate-determining steps

Reaction Bottlenecks in Chemical Kinetics

Reaction bottlenecks help explain rate-determining steps in multistep reaction mechanisms. In a mechanism with several elementary steps, one step is often much slower than the others. That slowest step is called the rate-limiting step, or rate-determining step. A reaction cannot move faster than its slowest step, so this step controls the overall reaction rate. The idea is like traffic on a four-lane freeway with one lane closed. Cars can only move as fast as the bottleneck allows. In the same...

catalysis

Catalyst Action in Reaction Rates

Catalysts change the rate of a chemical reaction by giving it a faster path. A catalyst increases reaction rate without being consumed during the process. Its effect is often explained with reaction mechanisms and energy diagrams. For an endothermic reaction, the reactants and products start and end at the same energies in both cases. The uncatalyzed path is a one-step mechanism with one transition state. The catalyzed path follows a different mechanism with two transition states and a lower...

enzymes

Enzyme Action and Inhibition

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase. Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and...

key terms and concepts

Learn how concentration affects reaction rate, how rate laws are written, and how initial rates reveal reaction order, the rate constant, and overall order.

Reaction Order from Concentration | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

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North Carolina K-12 Science Standard Course of Study

9-12

Matter and its Interactions

PS.Chm.5.1

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

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CH.7

CH.7.e

Minnesota Academic Standards in Science

3.2.1 9C.3.1.1.2

Arizona Science Standards

HS.P1

HS.P1U1.3

Next Generation Science Standards

Matter and Its Interactions

HS-PS1-4

HS-PS1-5

Florida Department of Education

SC.912.P.12

SC.912.P.12.12

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

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IPC.7.D

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Reaction Order from Concentration

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