Name: catalyst action in reaction rates
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 50 s
Channel: JoVE

K12 Standards

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

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.1

Catalysis

Reaksiyon mekanizmaları ve kinetik çalışmaları, araştırmacıların bir reaksiyonun hızını optimize etmelerine yardımcı olur. Sıcaklık veya konsantrasyondaki bir artış, hızı artıracaktır, ancak çok fazla arttığında ayrışmaya veya yan ürünlere de yol açabilir. Alternatif olarak, reaksiyon karışımına kalıcı olarak değiştirilmeden veya tüketilmeden reaksiyon hızını hızlandıran bir kimyasal ilave edilebilir.Bu maddelere katalizör adı verilir ve aktivasyon enerjisini değiştirerek hız sabitini etkiler. Aktivasyon enerjisi ne kadar yüksekse reaksiyon hızının o kadar yavaş olduğunu hatırlayın. Bu nedenle, sulu hidrojen peroksitin ayrışması gibi birçok kimyasal reaksiyon yavaş ilerler.Bir katalizörün eklenmesi, reaktanların ve ürünlerin enerji durumlarını etkilemeden alternatif bir reaksiyon mekanizması sağlayarak aktivasyon enerjisini düşürür. İki tür katalizör vardır homojen ve heterojen. Reaktiflerle aynı fazda olan katalizör homojen katalizör olarak adlandırılır.Örneğin, sodyum bromür, gaz halindeki oksijen ve suya ayrışmasını hızlandırmak için sulu hidrojen peroksite eklenir. İlk olarak, bromür iyonları, turuncu renkli bir sulu brom ve su çözeltisi oluşturmak için asidik bir ortamda hidrojen peroksit ile reaksiyona girer. Daha sonra sulu brom ve hidrojen peroksit reaksiyona girer ve renksiz bir çözelti ile gösterilen bromür iyonlarını serbest bırakır.Bir katalizör için karakteristik olan bromür iyonları reaksiyonu hızlandırır, ancak tüketilmeden kalır ve net dengeli denklemde görünmez. Reaksiyona girenlere kıyasla farklı bir fiziksel durumda heterojen bir katalizör bulunur. Heterojen kataliz, dört temel adımla karakterize edilir adsorpsiyon, difüzyon, reaksiyon ve desorpsiyon.Örneğin, doymamış eten gazının etana hidrojenasyon reaksiyonu, odun kömürü üzerinde ince bir şekilde dağılmış paladyum ile hızlandırılır. Burada, katalizör katı halde bulunurken, reaktanlar gaz halindedir. Bu heterojen kataliz sırasında, eten ve hidrojen molekülleri katalizör yüzeyine adsorbe olur.Hidrojen-hidrojen bağı kopar ve hidrojen atomlarının katalizör yüzeyinde dağılmasına izin verir. Difüze olan hidrojen atomları adsorbe edilmiş eten molekülleri ile karşılaştıklarında, doymuş etan oluşturmak için reaksiyona girerler. Daha sonra ürünler desorbe olur ve metal yüzeyden uzaklaşarak sağlam katalizörü geride bırakır.

kataliz

Bir katalizörün varlığı, bir kimyasal reaksiyonun hızını etkiler. Katalizör, işlem sırasında tüketilmeden reaksiyon hızını artırabilen bir maddedir. Kimyasal reaksiyonlar sırasında katalizör rolünün temel bir kavrayışı, reaksiyon mekanizmaları ve enerji diyagramları kavramından anlaşılabilir.
 
 <img alt=""Image1"" src=""/files/ftp_upload/11383/11383_Image_1.png"" style=""text-align: center; height: 350px;"" />
 
 Gösterilen görüntü, bir katalizörün yokluğunda (kırmızı eğri) ve varlığında (mavi eğri) ilerleyen bir endotermik kimyasal işlem için reaksiyon diyagramlarını temsil eder.
 
 Her iki eğri de aynı genel reaksiyonu temsil eder – aynı enerjilerde başlar ve biter. (Bu durumda, ürünler reaktanlardan daha fazla enerjiye sahiptir. Bu nedenle, reaksiyon endotermiktir). Bununla birlikte, reaksiyon mekanizmaları farklıdır. Katalize edilmemiş reaksiyon, tek adımlı bir mekanizma ile ilerler (sadece bir gözlenen geçiş durumu ile). Bunun tersine, katalize reaksiyon, özellikle daha az aktivasyon enerjisi ile iki aşamalı bir mekanizma (iki geçiş durumu gözlenir) izler. Reaksiyon yollarındaki bu fark, katalizörün daha düşük aktivasyon enerjisine sahip alternatif bir reaksiyon mekanizması sağlamadaki ve dolayısıyla reaksiyonları hızlandırmadaki rolünü gösterir.
 
 Katalize reaksiyon mekanizmasının, katalize edilmemiş mekanizmadan daha fazla sayıda temel adım içermesi gerekmez. Bununla birlikte, hız belirleme adımı, daha hızlı olan alternatif bir reaksiyon yolu sağlamalıdır (daha düşük bir Ea veya aktivasyon enerjisi ile).
 
 Katalitik bir reaksiyon, katalizörlerin ve reaktanların katalitik süreç sırasında var olduğu fiziksel durumlara bağlı olarak homojen veya heterojen olarak kategorize edilebilir.
 
 Homojen Kataliz
 
 Homojen katalizde, katalizör reaktanlarla aynı fazda –katı, sıvı veya gaz– bulunur. İşlem sırasında, katalizör bir ara madde oluşturmak için reaktanla etkileşime girer ve daha sonra orijinal katalizörü yeniden oluşturmak ve nihai ürünü oluşturmak için bir veya daha fazla adımda başka bir reaktanla reaksiyona girer.
 
 Homojen katalize bir örnek, dünyanın üst atmosferinde meydana gelen ozonun ayrışmasını içeren kimyasal süreçtir. Ozon, diatomik oksijen vermek üzere ayrışan nispeten kararsız bir moleküldür. Bu ayrıştırma reaksiyonu, aşağıdaki iki aşamalı mekanizma ile uyumludur:
 
 <img alt=""Eq1"" src=""/files/ftp_upload/11383/11383_Equation_1.png"" style=""text-align: center; height: 75px;"" />
 
 Pek çok madde ozonun ayrışmasını katalize edebilir. Örneğin, ozonun nitrik oksitle katalize edilen ayrışmasının aşağıdaki üç aşamalı mekanizma yoluyla meydana geldiğine inanılmaktadır:
 
 <img alt=""Eq2"" src=""/files/ftp_upload/11383/11383_Equation_2.png"" style=""text-align: center; height: 115px;"" />
 
 Bununla birlikte, genel reaksiyon hem iki aşamalı katalize edilmemiş mekanizma hem de üç aşamalı katalize edilmemiş mekanizma için aynıdır:
 
 <img alt=""Eq3"" src=""/files/ftp_upload/11383/11383_Equation_3.png"" style=""text-align: center; height: 50px;"" />
 
 Katalize edilen reaksiyonda, NO'nun mekanizmanın ilk adımında bir reaktan ve son adımda bir ürün olduğuna dikkat edin. Bu, bir katalizörün bir başka karakteristik özelliğidir: Kimyasal reaksiyona katılmasına rağmen, reaksiyon tarafından tüketilmez. Ek olarak, bu homojen katalizde, hem reaktan hem de katalizör gaz halinde bir fazda bulunur.
 
 Heterojen Kataliz
 
 Heterojen katalizde, katalizör reaktanlardan farklı bir fazda (genellikle katı) bulunur. Bu tür katalizörler genellikle bir reaksiyonun meydana gelebileceği aktif bir yüzey sağlayarak işlev görür. Heterojen katalizörler tarafından katalize edilen gaz ve sıvı faz reaksiyonları, gaz veya sıvı faz içinde değil, katalizör yüzeyinde meydana gelir.
 
 Heterojen kataliz tipik olarak aşağıdaki işlemleri içerir:
 <ol>
 <li>Katalizörün yüzeyindeki reaktan(lar)ın adsorpsiyonu</li>
 <li>Adsorbe reaktan(lar)ın aktivasyonu</li>
 <li>Adsorbe reaktan(lar)ın reaksiyonu</li>
 <li>Katalizörün yüzeyinden ürün(ler)in desorpsiyonu</li>
 </ol>
 
 <img alt=""Image2"" src= ""/files/ftp_upload/11383/11383_Image_2.png"" style=""text-align: center; height: 250px;"" />
 
 Gösterilen görüntü, etan gazı oluşturan katı bir nikel yüzeyinde etilen ve hidrojen gazının heterojen katalizini içeren reaksiyon mekanizmasını temsil eder (C2H4 +H2⟶ C2H6):
 
 (a) Hidrojen nikel yüzeyinde adsorbe olur. İşlem sırasında, hidrojen-hidrojen bağları nikel-hidrojen bağları oluşturmak için kırılır. 
 (b) Etilen ayrıca karbon-karbon pi-bağını kırarak ve nikel-karbon bağları oluşturarak nikel yüzeyinde adsorbe olur. 
 (c) Hidrojen atomları yüzey boyunca dağılır ve etan oluşturmak için çarpıştıklarında yeni karbon-hidrojen bağları oluştururlar (C2H6). 
 (d) Etan molekülleri nikel yüzeyinden desorbe edilir.
 
 Heterojen kataliz, amonyak, nitrik asit, sülfürik asit ve metanol gibi kimyasal ürünleri endüstriyel olarak üretmek için kullanılır. Benzinle çalışan otomobillerin çoğunda bulunan katalitik konvertörlerde de heterojen katalizörler kullanılmaktadır.
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href=""https://openstax.org/books/chemistry-2e/pages/12-7-catalysis"" > Openstax, Chemistry 2e, Section 12.7: Catalysis</a>

Kataliz

Bir katalizörün varlığı, bir kimyasal reaksiyonun hızını etkiler. Katalizör, tüketilmeden reaksiyon hızını artırabilen bir maddedir ...

Education

JoVE Core

Kimya

Chemical Kinetics

Kimyasal Kinetik

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 activation energy, or Ea. The lower rate-determining barrier is what makes the reaction faster.

Catalytic reactions are often grouped as homogeneous or heterogeneous. In homogeneous catalysis, the catalyst and reactants are in the same phase, which may be solid, liquid, or gas. The catalyst reacts with the reactant to form an intermediate, and that intermediate then breaks down or reacts again to form the product and regenerate the catalyst.

A good example of homogeneous catalysis is ozone decomposition in the upper atmosphere. Ozone breaks down to form diatomic oxygen, and nitric oxide can catalyze that process through a three-step mechanism. In this reaction, NO appears as a reactant in the first step and a product in the last step, which shows that it participates in the reaction but is not used up. Here, both the reactant and the catalyst are gases.

In heterogeneous catalysis, the catalyst is in a different phase from the reactants, usually a solid. These reactions happen on the catalyst surface. They typically include adsorption of reactants, activation on the surface, reaction of the adsorbed molecules, and desorption of the products.

The nickel-catalyzed reaction of ethene and hydrogen to form ethane shows this surface process. Hydrogen first adsorbs on nickel, and the H-H bond breaks to form nickel-hydrogen bonds. Ethene also adsorbs as its carbon-carbon pi bond breaks and nickel-carbon bonds form. Hydrogen atoms then move across the surface and make new carbon-hydrogen bonds, and the ethane product desorbs from the nickel surface.

Heterogeneous catalysts are important in industry. They help make ammonia, nitric acid, sulfuric acid, and methanol. They are also used in catalytic converters in most gasoline-powered cars.

Catalyst Action in Reaction Rates

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

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...

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

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

Explore how catalysts speed up reactions by lowering activation energy, with clear examples of homogeneous and heterogeneous catalysis for high school chemistry.

Catalyst Action in Reaction Rates | 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.

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

HIgh School

CH.7

CH.7.f

Arizona Science Standards

High School

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

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

Georgia Standards of Excellence

SC4.

Catalysts in Chemical Reactions

Scientific Laws and Theories

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Nuclear Power

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Nuclear Fusion

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Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

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The Pauli Exclusion Principle

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Electron Configuration of Multielectron Atoms

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PS.Chm.1.3

Periodic Classification of the Elements

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Molar Mass

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PS.Chm.2.1

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Atomic Radii and Effective Nuclear Charge

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Ionic Radii

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Ionization Energy

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Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

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Lewis Symbols and the Octet Rule

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Ionic Bonding and Electron Transfer

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The Born-Haber Cycle

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Resonance

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Formal Charges

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Exceptions to the Octet Rule

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	...

Bond Energies and Bond Lengths

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

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Intermolecular vs Intramolecular Forces

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Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Catalyst Action in Reaction Rates

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