Name: tracking reaction kinetics with light and pressure
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 3 min 9 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.F

Measuring Reaction Rates

Reaksiyon hızları, yani reaktanların veya ürünlerin konsantrasyonlarındaki değişiklikleri zamanın bir fonksiyonu alarak incelenebilir. Konsantrasyon değişiklikleri, polarimetre, spektroskopi veya basınç ölçümleri gibi deneysel tekniklerle ölçülebilir. Polarimetri, yalnızca bir düzlem boyunca yönlendirilmiş bir elektrik alanı ile düzlem polarize ışık kullanır.Bileşiklerin, mevcut bileşiğin moleküler yapısına bağlı olan polarize ışığı döndürme yeteneğini ölçer. Glikoz ve fruktoz üreten sakkarozun hidrolizini düşünün. Reaksiyona giren sakkaroz çözeltisinden gelen düzlemsel polarize ışığın dönme derecesini ölçmek için bir polarimetre kullanılır.Sakkaroz saat yönünde dönmeye neden olurken, glikoz ve fruktoz saat yönünün tersine dönmeye neden olur. Ayarlanan zaman aralıklarında ışığın dönme derecesinin ölçülmesiyle, bağıl sakkaroz, glikoz veya fruktoz konsantrasyonları hesaplanabilir ve reaksiyon hızı belirlenebilir. Reaksiyon hızları, reaktanların veya ürünlerin belirli dalga boylarındaki ışığı absorbe etme kabiliyetinden yararlanılarak, spektrofotometrik yöntemler kullanılarak da ölçülebilir.İlgi konusu maddenin konsantrasyonu ne kadar yüksekse, ışık emilimi o kadar yoğun olacaktır. Örneğin, renksiz hidrojen gazı, renksiz hidrojen iyodür oluşturmak için mor iyot buharı ile reaksiyona girer. İyot buharı, sarı-yeşil bölgedeki ışığı emer ve mor ışığı yansıtır.Reaksiyon sırasında, bir spektrofotometre numune tarafından emilen ışık miktarını ölçer ve toplanan ışığı analiz eder. Böylece reaksiyon ilerledikçe, sarı-yeşil ışık absorbansının azalmasıyla iyot buharı konsantrasyonunda azalma gözlenir. Beer-Lambert yasasını kullanarak, farklı zaman noktalarında absorblanan ışığın yoğunluğu hesaplanır ve konsantrasyondaki değişiklikle ilişkilendirilir.Alternatif olarak, reaktanlardan veya ürünlerden biri bir gaz ise, basınç değişikliklerini izleyerek reaksiyon hızlarını belirlemek için basınç ölçümleri kullanılır. Örneğin, hidrojen peroksit ayrışması sırasında, reaksiyon hızı, salınan oksijen gazının basıncını izlemek için bir manometre kullanılarak incelenir. Reaksiyon ilerledikçe ve daha fazla oksijen gazı geliştikçe, basınç yükselir.İdeal gaz denklemi kullanılarak farklı zaman noktalarında kaydedilen basınç değerleri konsantrasyonlara dönüştürülür. Zamanın bir fonksiyonu olarak konsantrasyondaki değişiklik, reaksiyon hızını belirlemek için kullanılır. Uzun süreli reaksiyonlar için, reaksiyon karışımından düzenli zaman aralıklarında numuneler veya alikotlar alınabilir.Bağıl konsantrasyonlar daha sonra reaksiyon hızlarını hesaplamak için gaz kromatografisi, kütle spektrometrisi veya titrasyon gibi enstrümental teknikler kullanılarak ölçülür.

reaksiyon hızını Ölçme

Polarimetri, bir kimyasal reaksiyon sırasında optik olarak aktif maddelerin konsantrasyonunu ve reaksiyon kinetiğini ölçmek için kimyasal kinetikte uygulama bulur. Optik olarak aktif maddeler, içlerinden geçen doğrusal polarize ışığın polarizasyon düzlemini döndürme kabiliyetine sahiptir — optik rotasyon adı verilen bir özellik. Optik aktivite, maddelerin moleküler yapısına atfedilir. Normal monokromatik ışık kutupsuzdur ve yayılma yönüne dik olan tüm olası düzlemlerde elektrik alan salınımlarına sahiptir. Polarize olmayan bir ışık bir polarizörden geçtiğinde, bir düzlemdeki salınımları koruyan doğrusal polarize bir ışık ortaya çıkar.
 
 Bir polarimetre aleti, ışığın polarizasyon yönünü veya optik olarak aktif bir maddenin ürettiği dönüşü belirler. Bir polarimetrede, düzlem polarize ışık, reaksiyona giren çözeltiyi içeren bir tüpe verilir ve reaksiyon, sistemi bozmadan takip edilebilir. Numune optik olarak inaktif maddeler içeriyorsa, polarize ışığın düzleminin yöneliminde herhangi bir değişiklik olmayacaktır. Işık, analizör ekranında aynı yoğunlukta görünecek ve dönüş açısı okuma (ɑ) sıfır derece okuyacaktır.
 
 Bununla birlikte, reaksiyona giren numunede optik olarak aktif bileşiklerin varlığı, içinden geçen polarize ışığın düzleminin dönmesine neden olur. Dışarı çıkan ışık daha az parlak olacaktır. Analiz cihazı cihazının ekseni, maksimum parlaklığı gözlemlemek için saat yönünde (sağa döndürülen) veya saat yönünün tersine (sağa döndürülen) yönde döndürülmelidir. Analizörün döndürülmesi gereken yön, mevcut bileşiğin yapısına bağlıdır. Ölçülen optik rotasyon, numunede bulunan optik olarak aktif maddelerin konsantrasyonu ile orantılıdır. Farklı zaman noktalarında dönme açısı ölçümlerini analiz ederek, optik olarak aktif bileşiklerin konsantrasyonları zamanın bir fonksiyonu olarak belirlenebilir.
 
 Spektrometre
 
 Spektrometri gibi optik deneysel teknikler, kimyasal reaksiyonları izlemek ve reaksiyon kinetiğiyle ilgili niceliksel bilgileri güvence altına almak için sıklıkla kullanılır. Spektrometri kullanılarak, belirli bir dalga boyunun ışığının reaksiyona giren bir numuneden geçmesi sağlanır. Numune içindeki moleküller veya bileşikler (bir reaktan veya ürün), bir detektör tarafından ölçülen kalan miktarı iletirken bir miktar ışığı emebilir. Emilen ışığın miktarı, ilgilenilen bileşiğin veya molekülün konsantrasyonuna bağlıdır. Örneğin, bir bileşiğin konsantrasyonu ne kadar yüksekse, absorbansı da o kadar büyük olur. Absorbanstan, cihaz ilgilenilen bileşiğin konsantrasyonunu belirleyebilecektir. Reaksiyona giren bir numunede, periyodik aralıklarla ölçülen absorbans, reaktan veya ürünün konsantrasyonlarını zamanın bir fonksiyonu olarak hesaplar.
 
 Basınç Ölçümleri
 
 Gaz fazındaki maddeleri içeren reaksiyonlar için, reaksiyon kinetiğini, basınçtaki değişikliklerin bir fonksiyonu olarak gazların mol sayısındaki değişikliklerin ölçülmesi izler. Bir gaz fazı reaksiyonunun deneysel ayarları, gaz halindeki bir reaktantın veya ürünün basıncını ölçebilen bir manometreye bağlanabilir. Reaksiyon ilerledikçe, reaktanların basıncı azalır ve (veya) ürünlerin basıncı artar. Bu, zamanın bir fonksiyonu olarak manometre ile ölçülebilir. İdeal gaz yasasını kullanarak (bir gazın konsantrasyonu, kısmi basıncıyla orantılıdır) bir kimyasal reaksiyonun hızı hesaplanabilir.

Reaksiyon Hızını Ölçme

Polarimetri, bir kimyasal işlem sırasında optik olarak aktif maddelerin konsantrasyonunu ve reaksiyon kinetiğini ölçmek için kimyasal kinetikte uygulama bulur.

Education

JoVE Core

Chemistry

Kimya

Chemical Kinetics

Kimyasal Kinetik

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

tracking reaction kinetics with light and pressure

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 through a polarizer, it becomes linearly polarized with vibrations in one plane.

In a polarimeter, this plane-polarized light is sent through a tube of reacting solution. The instrument then shows how much the light has been rotated. If the sample contains optically inactive substances, the light keeps the same orientation, the analyzer screen stays equally bright, and the rotation angle is zero degrees. If optically active compounds are present, the light becomes dimmer and the analyzer must be turned clockwise or counter-clockwise to restore maximum brightness. Clockwise rotation is dextrorotatory, and counter-clockwise rotation is levorotatory.

The amount of optical rotation is proportional to the concentration of the optically active substance in the sample. By taking rotation readings at different times, the concentration can be followed as the reaction proceeds. Spectrometry gives similar kinetic information by passing light of a specific wavelength through a reacting sample. Some of the light is absorbed by the reactant or product, and a detector measures the remaining light. Higher concentration gives higher absorbance, so repeated absorbance measurements can be used to find concentration over time.

Pressure measurements are useful for gas-phase reactions. A manometer can be connected to the reaction setup to monitor the pressure of a gaseous reactant or product. As the reaction goes on, reactant pressure may decrease and product pressure may increase. Using the ideal gas law, the concentration of a gas is proportional to its partial pressure, so reaction rate can be calculated from the pressure change.

Tracking Reaction Kinetics with Light and Pressure

tracking-reaction-kinetics-with-light-and-pressure

reaction rate

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

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

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

Collision theory explains why reaction speed depends on how particles collide. Atoms, molecules, or ions must come close together before they can react. The theory says the reaction rate depends on the collision rate, the orientation of the colliding species, and whether the collision has enough energy for bonds to change. A gas-phase reaction between carbon monoxide and oxygen shows why orientation matters. The molecules can collide in more than one way. If the oxygen side of carbon monoxide...

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...

reaction mechanisms

Elementary Steps in Reaction Mechanisms

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

See how polarimetry, spectrometry, and pressure measurements monitor reaction kinetics by tracking optical rotation, absorbance, and gas pressure changes.

Tracking Reaction Kinetics with Light and Pressure | JoVE K12

chemistry

JoVE Core Kimya, özlü ve kolay anlaşılır animasyon video derslerini kullanarak genel kimya kavramlarına hayat veriyor. Ek olarak, bilim insanı uygulama videolarımız ile klasik ve orijinal araştırma deneylerini dünya çapında günümüz laboratuvarlarında görselleştiriyoruz.

north-carolina-k-12-science-standard-course-of-study

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

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.e

Minnesota Academic Standards in Science

3.2.1 9C.3.1.1.2

Alabama Course of Study Science

Matter and Its Interactions: Energy

9-12.C.3.3.d

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.B

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IPC.7.D

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Tracking Reaction Kinetics with Light and Pressure

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