Jiwei Li and Tatiana Vrabie

Of Jiwei Li and Tatiana Vrabie

Chemistry, Grade 12, University Preparation SCH4U

Concept presentation: Rate of Reaction

Summary

Background Information

Slow Reaction Fast Reaction http://en.wikipedia.org/wiki/Reaction_rate

The reaction rate represents the speed of reaction or the speed of chemical change. It may be measured by the amount (usually expressed in moles) or concentration of substance transformed/changed/produced in the unit of time.

For example, 2Mg(s) + O2 → 2 MgO(s) In this reaction, we can observe how much time is necessary for all amount of magnesium to react with oxygen.

The average rate (r) of a reaction is expressed as the number of moles of Mg used up or MgO formed, divided by the total reaction time:

c Mg MgO r     t t t

The instantaneous rate of reaction is the speed at particular moment (point) of reaction, can be obtained from the slopes of the tangents to the line of concentration vs time.

Chemists are equipped with different methods to measure the rates of reactions, which are merely quantitative analysis of substance vs. time. The most important are volume for gases with low solubility, conductivity for ions, spectrophotometry for light absorbing substances in solutions. The most important factor for the speed of reaction is concentration of reactant. It is a common sense that more particles (molecules, ions, atoms) we have at the beginning of change (reaction), the more changed particle we can observe in the unit of time. That’s why speed is a function of reactant initial concentration. The name of function is Rate Law and reactions are classified by Rate Law in order 0, 1, 2.

For reaction aX + bY → product, the Rate Law or Rate Equation is: r  kX m Y n , where {X}, {Y} are known initial concentrations and k –rate constant; m, n –exponents or individual orders of reaction, determined empirically. Overall order of reaction is equal to m+n.

Five factors are affecting Rates of Reaction (RR):  Nature of reactant  Concentration raise increases RR  Temperature raise increases RR  Presence of a Catalyst increases RR  Surface area raise increases RR

Why all these factors are important is explained by Collision Theory. The main concepts of Collision Theory are:

 The average kinetic energy of particle is proportional to temperature of sample  Collisions of particles is a must for reaction to occur  Only collision of particles with sufficient energy leads to successful reaction  RR depends on frequency of collisions and the fraction of successful collisions

A reaction mechanism is a series of steps that make up an overall reaction. Each step, called an elementary reaction, involves a single molecular event, such as a simple collision between atoms, molecules, or ions. Usually the elementary reaction called rate-determining step determines the overall rate.

Molecularity Elementary step Rate law 1 A -> products rate = k [A] A + A -> products rate = k [A]2 2 A + B -> products rate = k [A] [B] A + A + A -> products rate = k [A]3 3 A + 2 B -> products rate = k [A] [B]2 A + B + C -> products rate = k [A] [B] [C]

A catalyst is a substance that increases the rate of a chemical reaction without being consumed by the reaction. A catalyst works by lowering the activation energy of a reaction so that a larger fraction of the reactants have sufficient energy to react. A homogeneous catalyst exists in the same phase as the reactants. Homogeneous catalysts most often catalyze gaseous and aqueous reactions. A heterogeneous catalyst exists in a phase that is different from the phase of the reaction it catalyzes.

Curriculum expectations

D2.8 plan and conduct an inquiry to determine how various factors (e.g., change in temperature, addition of a catalyst, increase in surface area of a solid reactant) affect the rate of a chemical reaction [IP, PR, AI]

D3.5 explain, using collision theory and potential energy diagrams, how factors such as temperature, the surface area of the reactants, the nature of the reactants, the addition of catalysts, and the concentration of the solution control the rate of a chemical reaction

Advance Preparation

Prerequisite for Rate of Reaction unit is knowledge about Enthalpy and Heats of Reaction as well as Hess’s Law and Thermochemical Equations. Many lessons include computer simulations, therefore computers availability should be arranged in advance. For Lab Activities students should be asked to bring lab coats, goggles and gloves. Video demonstration require teacher to check up Internet and projector function in the classroom

For the Project or Thought Lab, teacher should come to class prepared with several suggestions of catalysts and enzymes. Therefore, teacher may need to do some initial research.

Teaching Ideas / Strategies / Lesson sequence

Lesson Title Classroom activities Learning/Teac Assessment & Number hing Strategy strategy, Achievement category 1. Expressing Thinking about slow and fast reactions, for example: Brainstorm, AF*Anecdotal and rusting of metals, weathering of rocks (e.g. limestone rocks Whole class notes, Questions Measuring being weathered by water), combustion. activity and Answers, Reaction K/U Rates Class Demo: Mg and Fe reactions with HCl. Students Demonstration AF, figure out reactions equations and predict the RR. Cooperative Peer evaluation, http://www.infoplease.com/chemistry/simlab/singlehcl.htm groups T, A, C l lab simulation, single replacement reactions with different Computer metals. simulation

Expression of RR, average, instantaneous rate, calculating Direct AA, the rates. instruction Flash-cards main points, Q&A, K/U Calculations of RR. Practice p.364#1, 2, 3{1} Problem AA, Solving Numerical In cooperative Problem Solving groups T/I, A, C Measuring RR. Reactions that produce a Gas, involves Lecture brief AA, Q&A on Ions, change Color methods of measuring K/U, T Homework: p.365#4, 5, 6; p.366#1 Independent AO, work Self assessment, K/U, T, A 2. The Rate Video http://www.youtube.com/watch?v=kjKyEdrVXJA Lab. Activity in AO, Law and demo”the rate vs conc.” cooperative Lab Report, Order of Investigation 6.3.1. The Iodine Clock Reaction. {1} to find groups Performance Reaction empirically RR as function of initial concentration and checklist, and on- formulate Rate Law equation. the-spot http://www2.ucdsb.on.ca/tiss/stretton/chem2/ratelab1.htm questioning worksheets for Lab. K/U, A, C, T/I Rate law, Rate Law equation, order of reactions (individual Anticipation AF, AA, and overall), Half-life. Guide, Checklist on independent Anticipation reading and Guide Questions, discussion in K/U, T group http://www.chm.davidson.edu/vce/kinetics/DifferentialRate Computer AA, Laws.html simulation Q&A, (order of K/U reaction, half- life) Finding the order of reaction and Half-life. Practice: p. Problem AO, 377#2, 3. {1}; p.381#3 solving in Numeric Problem cooperative solving, peer groups evaluation, T/I, A, C, K/U 3. Theories Factors affecting RR, animation. Computer of http://www.concord.org/activities/chemical-reactions-and- simulation Reaction stoichiometry (temp., conc., Rates surface area factors). Gizmo Worksheet “Collision Theory” and animations Problem AA, (Activities A and B) solving on Worksheet http://www.explorelearning.com/index.cfm? worksheets checklist, method=cResource.dspDetail&ResourceID=553 Think-Pair- T/I, A, C Share Concepts of the Collision Theory, Kinetic energy, Lecture brief AO, activation energy, endo- and exo- termic reactions, Concept Map Short Quiz, theoretical effect of conc, surface area, temperature. http://jsteinwe K/U, A, C, T/I bsite.yolasite. com Homework:Practice p.387#1 {1} AO, Independent Self-assessment work K/U, A, C

Lecturing the concepts of reaction mechanism, Lecturing K/U, C 4. Reaction elementary reaction, rate–determining step. Questioning Mechanis ms and Groups working on the practice problems Jig-saw activity AO Catalysts p.301 #17-20{2} Participation action K/U, C Lecturing the concepts of catalyst (heterogeneous and Brainstorming homogeneous) and how a catalyst works. Computer http://www.concord.org/activities/catalysts animation AO, Homework: section review p.309 #6-9 Independent Self-assessment Work K/U, T/I, C 5. Lab Inquiry-based lab. Group work AO investigati In this lab activity students will examine some of the key Lab activity Lab on factors that influence the rate of a reaction: Critical thinking performance  nature of reactants - particle size K/U, T/I, A, C  temperature  concentration  catalysts

Students are given the lab materials and then asked to design the procedure by themselves.

The lab can be obtained from: http://www.saskschools.ca/curr_content/chem30_05/2 _kinetics/labs/rate_factors.pdf AO Homework: Lab Report Rating Scale K/U, T/I, C 6. Project Developing a Bulletin About Catalyst and Enzymes Students STSE AO Design an information bulletin to inform the project The bulletin community about the use of catalysts or enzymes in presentation should be Canadian industries. Do the research interesting, The project should contain the following analysis: on internet or in visually For catalyst: library, collect attractive , (a) What is the chemical formula of the catalyst? Is the catalyst data and heterogeneous or homogeneous? information and factual, and (b) What process does the catalyst speed up? Include products, aimed at a wide reactants, the reaction mechanism (if possible), and information evaluate the about the uncatalyzed reaction. information audience. (c) What technology is required to support the catalyzed reaction Students’ (for example, the design of a catalytic converter)? designed rubric (d) What is the importance and relevance, to Canadians, of the industry associated with the catalyst? for multiple For enzyme: intelligence (a) What chemical process is the enzyme involved in? (song, essay, (b) How does the enzyme fit into an overall biological process? (c) Are there any ways in which the enzyme can be prevented diary entry, from doing its job? Explain. visual design, (d) Is the enzyme mass-produced by industry? If so, how? For what purpose is it mass-produced? role play performance, A, C

* Note: Assessment for Learning-AF, as Learning – AA, of Learning - AO

Potential students Difficulties and Possible Solutions

Potential Difficulties Possible Solutions

Students may mix up the To show in the lab. that reaction order is determined empirically and may stoichiometric coefficients be non-integer number, differentiate wit colors. with reaction order Give some example of non-integers order http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Reaction_Rates /Definition_of_Reaction_Order Finding Mathematical Give the students equation of a straight line and repeat how it may be expression for Iodine Clock found from plot. Rate of Reaction. Understanding that the Contrast and show by animation that frequency does not increase frequency of collisions is not essentially with temperature, but average energy of particle does, which is the function of temperature important for reaction to occur.

Misconception of catalyst and Asking students to brainstorm a list of what they already know. Address enzyme that catalysts and enzymes are regenerated unchanged at the end of a reaction, and they usually increase the rate of a reaction.

Differentiated Assessment

Differentiated Assessment should be provided to evaluate the learning outcome of Differentiated Teaching Strategies.

Diagnostic Assessment empowers students as well as teacher with better knowledge of their strength and weaknesses and helps create more successful learning plan. Diagnostic or Assessment for learning is done at the beginning of the unit in the form anecdotal notes during brainstorm, Q&A before and after Demo, checklist on answers on Anticipation Guide. Assessments as learning were used permanently as Numerical problems Solving, Questions and Answers, Worksheet answers checklist. This type of assessment serves for identification of difficulties, misconceptions and current results of students learning.

Assessment of learning was performed as self –assessment, Lab. Report, Performance Checklist, peer evaluation in numeric problem solving, short quiz. The purpose of AO is to gain evidence of students’ achievements in some tasks and skills.

The project of “Bulletin” can be alternated as a “Thought Lab”. In the lab, teacher helps students create a list of catalysts that are used in industries and a list of enzymes. Students choose one industrial catalyst and one enzyme (specific biological catalyst, which is protein by chemical nature) and use electronic and print resources to research the substances. They also can write a song, essay, diary entry, make visual design on poster or even create animation, role play performance, calculations and logical construction to fulfill the task.

Applications and Societal Issues/Implications

Many reactions that produce useful compounds proceed too slowly to be used in industries. Some reactions need to be carried out at high temperatures or pressures to proceed quickly. These conditions, however, are often expensive to maintain. Therefore, chemists and engineers use catalysts to speed up the reactions in order to obtain products at a reasonable rate and under mild conditions. Similarly, without the presence of enzymes many necessary biological reactions would proceed too slowly to sustain life. The primary action of most drug and vitamins is related to biochemical reactions rate, which is controlled through enzyme regulation. For specific purposes is beneficial to slow down chemical reactions, especially in food industry (food preservation reactants, storage in the cold conditions, in the liquid nitrogen, inert gases), inhibition of microorganisms growth, some surgical processes need cooling of body tissues. The project of “Bulletin” or “Thought Lab” is designed to study some applications and societal issues.

Accommodations

 consult individual student IEPs for specific accommodation and modifications in teaching methodologies  when grouping students take into account availability of peer help  help students with creation of graphic organisers  be cooperative with special education providers about tests, assignments, etc.  permit ESL/ESD students use translators and extend timelines for them  record keywords on a board  provide appropriate level resources for reading  use more visual aids http://resources.curriculum.org/csc/library/profiles/12/html/SCH4UP.htm

Safety Considerations • Teacher review the safety rules before lab and Students should have their lab coats, goggles and gloves ready for use. • As students will use computers to complete virtual labs and research, it is important that teacher ensures that students are using computer in an appropriate way. Annotated References

1. Van Kessel, H., Jenkins, F., Davies, L., Plumb, D., Di Giuseppe, M., Lantz, O., & Tompkins, D. (2002). Nelson chemistry 12. Toronto, Ontario: Nelson Thomson Learning.

2. Mustoe, F., Jansen M.P., Webb, M., Hayhoe, C., Cherkas, A., Gaylor, J. (2002) Chemistry 12 McGraw-Hill Ryerson

3. FHSST Authors. The Free High School Science Texts: Textbooks for High School Students Studying the Sciences. Chemistry, Grades 10 – 12. 2008 www.fhsst.org

4. http://www.woodrow.org/teachers/chemistry/exchange/topics/woc/woc14.html Collision Theory Quiz 5. 6. http://www.chm.davidson.edu/vce/kinetics/ReactionRates.html reaction rates simulations with background information.

7. http://www.infoplease.com/chemistry/simlab/singlehcl.html Virtual lab. simulation, single replacement reactions

8. http://www.concord.org/activities/chemical-reactions-and-stoichiometry Effect of temperature, concentration and surface area on RR, animation

9. http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=553 Gizmos worksheets and computer simulations on Collision Theory and other chemistry curriculum topics.

10. http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Reaction_Rates/Definition_of_Re action_Order Non-integer order of Chemical reaction, problem solving

11. http://www.youtube.com/watch?v=kjKyEdrVXJA Demo of H2O2 decomposition rate at concentration 3% and 30%

12. http://jsteinwebsite.yolasite.com Chemistry teacher Janet Stein website, some course outlines, worksheets, concept maps

13. http://www2.ucdsb.on.ca/tiss/stretton/chem2/ratelab1.htm Worksheet for lab. “The Iodine Clock Reaction”

14. http://www.chemguide.co.uk/physical/basicrates/ordermech.html#top rates of reaction, diagrams and explanations

15. http://www.saskschools.ca/curr_content/chem30_05/2_kinetics/labs/rate_factors.pdf Factors Affecting Reaction Rate

16. http :// www . concord . org / activities / catalysts activity addresses homogeneous catalysis Additional web resources http://resources.curriculum.org/csc/library/profiles/12/html/SCH4UP.htm Chem 12 all units Plans http://www.virtlab.com/Chapters/Chapter7.aspx virt lab, needs subscription payment http://www.aeei.gov.sk.ca/Default.aspx?DN=ab27fca2-315f-4e5c-8cd1-cc60061a2475 science

http://phet.colorado.edu/en/simulation/reactions-and-rates Interactive Simulations on rate of reaction

http://www.youtube.com/watch?v=A_PhvIktMOw&feature=related t video about Catalysis: introduce the concepts of Catalysis and how we use Catalysts in everyday scenarios http://www.slideshare.net/JSlinkyNY/reaction-rate concept presentation Concept Map (Rate of Reactions) SCH4U Curriculum Specific Expectations:

D3.5 explain, using collision theory and potential energy diagram, how factors such as temperature, the surface area of the reactants, the nature of the reactants, the addition of catalysts, and the concentration of the solution control the rate of chemical reaction.

Specific for this activity: Learning expectation: Demonstrate and refine understanding of “Rate of Reactions” concept and its connection to other concepts.

Time: 30 minutes, as a review activity

Materials:  A1 size paper – 1 for each students’ group  Set of small images with the names related to Rate of Reactions concepts – 1 set per group  Glue

Teaching strategies:

 Cooperative groups (3-4 students, numbered heads together) with assigned roles and numbers (Record Keeper, Materials Handler, Time Manager, Presenter)  Concept Map

Task: - Teacher will give explanation on Assessment format and materials distribution -5 min - Students will construct Concept Map on A1 size paper by using the given set of images and glue - 10 min - Students would indicate on arrow descriptive relationship between concepts - Each group will present their Concept Map and numbered heads would debates or stand by their way of presentation – 15 min For example:

Temperature →→→→Rate of Reaction (“Positive correlation” above the arrow)

Assessment:

 Anecdotal notes as formative assessment  Fool mark will be granted to all group members with condition that all members of group can explain Map design at minimum acceptable level  Achievement Rubric: K/U, T/I, C Collision Theory Quiz http://www.woodrow.org/teachers/chemistry/exchange/topics/woc/ woc14.html

1. What is the basis of all chemical reactions?

2. What is necessary for successful collisions?

3. What is meant by activation energy?

4. How are activation energies affected by catalysts?

5. What is true about a catalyst at the end of a chemical reaction?

6. What is meant by equilibrium?

7. What does Le Chatelier's Principle tell us about equilibrium reactions?

8. What is the reaction involved in the Haber Process?

9. Why is this reaction important? 10. What conditions are used to increase the yield in the Haber Process?

Answer Key

1. What is the basis of all chemical reactions?

Collisions of particles that have the minimum energy to react.

2. What is necessary for successful collisions?

The collisions must be of sufficient energy to react.

3. What is meant by activation energy?

The minimum amount of energy needed to bring about a reaction.

4. How are activation energies affected by catalysts?

They are lowered.

5. What is true about a catalyst at the end of a chemical reaction?

It remains unchanged.

6. What is meant by equilibrium?

Two opposing reactions that occur at equal rates.

7. What does Le Chatelier's Principle tell us about equilibrium reactions?

The reaction may be ``shifted'' when stresses are applied to the system.

8. What is the reaction involved in the Haber Process?

2 H2 + N2 2 NH3

9. Why is this reaction important?

Ammonia is an important starting material in the manufacture of fertilizers and explosives.

10. What conditions are used to increase the yield in the Haber Process?

The temperature was kept relatively low, the pressure was kept high Collision Theory http://jsteinwebsite.yolasite.com

Complete this concept map using these terms: collision theory, Temperature, concentration (of reactant molecules), reaction rates, catalyst, amount of energy

______explained by influenced by

______

______Complete this sentence:

1. Increasing the temperature will ______the number of effective collisions.

Write your answer to these questions in complete sentences:

2. Keeping a lightstick in the freezer prolongs its life because:

3. What is meant by an “effective collision”?

4. In addition to temperature, explain how a catalyst can affect the rate of a chemical reaction.