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

המדד למהירות שבה תגובה מתקדמת נקרא קצב התגובה. עבור תגובה חד-שלבית, הקצב שווה לשינוי בריכוז של כל מגיב או מכפלה לאורך זמן כפול ההופכי של המקדם הסטויכיומטרי המתאים. אפשר לחשוב על השינוי בריכוז לאורך זמן כעל הריכוז בזמן t פחות הריכוז ההתחלתי חלקי t. קצבי התגובה הם תמיד חיוביים, ולכן להבעות התגובה יש סימנים שליליים. שיעורים אלה עשויים שלא להיות שווים בתגובות מרובות שלבים, אך אנו עדיין יכולים להשתמש בקשר זה כהערכה לתגובה הכוללת.
חוק הקצב, או משוואת הקצב, מתאר את הקשר בין מהירות התגובה לבין ריכוזי המגיבים. במשוואה זו, k הוא קבוע הקצב, A ו-B הם שני המגיבים, ו-m ו-n הם סדרי התגובה שלהם. סדר תגובה מתאר את הקשר בין ריכוז המגיב לבין הקצב ואינו קשור לסטויכיומטריה. חשוב לזכור שסדר התגובה אינו זהה למקדם המגיב במשוואה המאוזנת.
כאשר תגובה מערבת שני מגיבים או יותר, עלינו לשקול את סדר התגובה עבור כל מגיב. סדר התגובה הכולל שווה לסכום פקודות התגובה של המגיבים. לדוגמה, אם מגיב A הוא מסדר ראשון ומגיב B הוא מסדר אפס, סדר התגובה הכולל הוא אחד. סדרי התגובה הנפוצים ביותר בתגובות פשוטות הם סדר אפס, סדר ראשון וסדר שני. בואו נעבור עליהם באמצעות תגובה חד-מולקולרית כדוגמה.
אם התגובה היא מסדר אפס, לריכוז המגיב אין השפעה על קצב התגובה. לפיכך, קצב התגובה שווה ל-k, קבוע הקצב. גרף של קצב התגובה ביחס לריכוז הוא קו אופקי.
ביחסים מסדר ראשון, ריכוז המגיב קשור באופן ליניארי לקצב התגובה. לפיכך, הקצב שווה לקצב קבוע כפול ריכוז המגיב. גרף של קצב התגובה ביחס לריכוז יהיה ליניארי, עם k כשיפוע.
אם התגובה היא מסדר שני, קיים יחס ריבועי בין הריכוז לבין הקצב. לפיכך, השיעור שווה לשיעור קבוע כפול הריכוז בריבוע. גרף של הקצב ביחס לריכוז יהיה פרבולי, עם k כשיפוע.
קבוע הקצב, k, הוא ערך תלוי טמפרטורה המקשר בין אנרגיית ההפעלה של התגובה לקצב התגובה. תוכלו לחקור זאת בניסוי המעבדה הבא.
קצבי התגובה ניתנים בדרך כלל בשומות לליטר לשנייה. לשיעור יש את אותן יחידות, ללא קשר לסדר התגובה. לפיכך, קבוע הקצב יש יחידות שונות, בהתאם לסדר התגובה. לדוגמה, אם A הוא מסדר ראשון ו-B הוא סדר אפס, אז יש לנו מופע אחד של שומות לליטר במשוואת הקצב. לכן, קבוע הקצב חייב להיות בשניות הפוכות.
אז איך קובעים את סדר התגובה? סדר התגובה חייב להיקבע באופן ניסיוני באמצעות סדרה של בדיקות. אם יש לך שני מגיבים, שיטה אחת היא להחזיק את הריכוז של מגיב אחד קבוע, לשנות את השני, ואת הזמן כמה זמן לוקח לייצר כמות מסוימת של תוצר. אותו תהליך חוזר על עצמו עבור המגיב השני. לאחר מכן ניתן להעריך את הסדר של כל מגיב על ידי התוויית קצב לעומת הריכוז המשתנה של המגיבים, ולראות אם הוא נראה כמו גרף מסדר אפס, ראשון או שני. התאמת הנתונים שלך למשוואת הקצב המתאימה תאפשר לך גם לחשב k.
במעבדה זו תקבעו את סדרי התגובה של שני מגיבים על ידי שינוי הריכוזים שלהם והתזמון כמה זמן לוקח לתגובה להתקדם עד להפיכת התמיסה לאטומה.

תלות בריכוז

קינטיקה כימית וחוק קצב התגובה
קינטיקה כימית מתייחסת לקצב או למהירות של תגובה כימית. הקצב תלוי במנגנון, במורכבות ובמספר המגיבים בתגובה. ריכוז המגיבים גם משחק תפקיד משמעותי בקצב התגובה.
חוק התעריף מכמת את הקשר הזה באמצעות ניסויים. כל מגיב תורם למהירות התגובה על ידי גורם המכונה סדר התגובה. גורם זה יכול לנוע בין אפס לשניים, וזה תלוי במערכת היחסים של אותו מגיב עם קצב התגובה.
r = k[A]m[B]n for aA + bB + ... → סמ"ק
במשוואה זו, r הוא קצב התגובה, k הוא קבוע קצב התגובה, [A] ו-[B] הם ריכוזי המגיבים A ו-B, ו-m ו-n הם סדרי התגובה של מגיבים A ו-B, בהתאמה. קצב התגובה, r, מוגדר כשינוי בריכוז המוצר עם הזמן ויש לו יחידות של שומות לליטר לשנייה.
<h4>סדר תגובה</h4>
סדר התגובה מתאר את תלות הכוח שיש לריכוז המגיבים בקצב התגובה. סדר התגובה הכולל הוא סכום פקודות התגובה עבור כל אחד מהמגיבים. חשוב לזכור שסדר התגובה אינו קשור לגורמים הסטויכיומטריים של המשוואה הכימית המאוזנת. במילים אחרות, לא ניתן להשתמש בסטואיכיומטריה כדי לקבוע את סדרי התגובה לתגובה כימית. סדרי התגובה חייבים להיקבע באופן ניסיוני
כדי לקבוע את סדר התגובה, הריכוז של המגיב השני מוחזק קבוע, בעוד הריכוז של המגיב הראשון הוא מגוון. הזמן שלוקח לתגובה להתרחש נמדד בשניות; עם זאת, זמן זה אינו תואם את הזמן שלוקח את התגובה ללכת להשלים. במקום זאת, זה הזמן שלוקח לתגובה להתחיל. לאחר מכן משווים את זמני התגובה של ריכוזי המגיבים השונים כדי לקבוע את הסדר. אותה סדרה של תגובות מבוצעות כדי לקבוע את הסדר של המגיב השני, שבו הריכוז של המגיב הראשון מוחזק קבוע והריכוז של המגיב השני משתנה.
על ידי השוואת זמני התגובה ניתן לקבוע את סדר התגובה. לדוגמה, אם זמן התגובה נשאר קבוע למרות השינויים בריכוז המגיב, אז המגיב הוא מסדר אפס. משמעות הדבר היא שקצב התגובה שווה למקדם קצב התגובה, k, שחייב להיות בעל יחידות של M/s. אם זמן התגובה משתנה באופן ליניארי עם שינויים בריכוז (כלומר, הכפלת הריכוז משפיעה על זמן התגובה בפקטור של 2), אז המגיב הוא מסדר ראשון. משמעות הדבר היא שקצב התגובה שווה למכפלה של מקדם קצב התגובה וריכוז המגיב. במקרה זה, k יש יחידות של 1/s. לבסוף, אם זמן התגובה מושפע מפקטור של 4 כאשר ריכוז המגיב מוכפל, המגיב הוא מסדר שני. משמעות הדבר היא שקצב התגובה שווה לקצב קבוע כפול ריבוע ריכוז המגיב, ויוצר קשר ריבועי. במקרה זה, היחידות של k חייבות להיות 1/M⋅s.
הסדר הכולל של התגובה הוא סכום פקודות התגובה הבודדות. לדוגמה, אם התגובה היא מסדר ראשון ביחס ל-A, אז m = 1. ואם התגובה היא מסדר אפס ביחס ל-B, אז n = 0. הסדר הכולל של התגובה הוא מסדר ראשון מכיוון ש- m + n = 1.
<h4>קבוע קצב תגובה</h4>
קבוע הקצב, k, הוא ספציפי לתגובה ולטמפרטורה שהתגובה מבוצעת. קבוע הקצב נקבע מסדרת הניסויים. באמצעות הקצב הנמדד וריכוזי המגיבים הראשוניים, משוואת הקצב משמשת לפתרון קבוע הקצב. קבוע הקצב תלוי בטמפרטורה ומוגדר על ידי משוואת ארניוס. משוואה זו מתארת את הקשר בין k לבין אנרגיית ההפעלה, Ea, הטמפרטורה, T, וקבוע הגז האידיאלי, R. הקבוע A הוא קבוע של מידתיות ואין לבלבל אותו עם מגיב A.
<img src="/CDNSource/lm/labs/50/50_Concepts_2.jpg">
<h4>הפניות</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). כימיה ותגובתיות כימית. בלמונט, קליפורניה: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). כימיה: הטבע המולקולרי של חומר ושינוי. בוסטון, מסצ'וסטס: מקגרו היל.</li>
</ol>

קינטיקה כימית וחוק קצב התגובה
קינטיקה כימית מתייחסת לקצב או למהירות של תגובה כימית. התעריף תלוי במנגנון, ...

Education

JoVE Lab Manual

כימיה

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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recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

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.

התכוננו ללמד את תלות בריכוז עם מדריך מדריכים זה באורך 5 דקות. כולל שלבי הכנה מרכזיים עבור מעבדת Chemistry ב-JoVE Lab Manual.

הכנת מדריך עבור תלות בריכוז ב-Chemistry - 2.2K+ צפיות | JoVE Lab Manual

עקבו אחר הנהלים של תלות בריכוז שלב אחר שלב בסרטון פרוטוקול סטודנטים זה באורך 10 דקות. חלק מאוסף Chemistry ב-JoVE Lab Manual.

פרוטוקול סטודנטים עבור תלות בריכוז ב-Chemistry - 4.4K+ צפיות | 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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