Teaching the Concept ofTeaching the Concept ofRates of Chemical ReactionsRates of Chemical ReactionsBy: Tatiana Vrabie & Jiwei LiBy: Tatiana Vrabie & Jiwei Li

Introduction to Reaction RatesIntroduction to Reaction Rates Before studying reaction rates, students may imagine

that most reactions occur very quickly, and proceed to completion. However, Some reactions do not occur at all under most conditions , and others are very slow.

What makes some reactions occur within a few seconds while others occur over days, or even years?

What can you do to speed up or slow down a reaction? Why do factors such as temperature, surface area, and concentration affect reaction rates?

Students will answer these questions and others as they learn about the rates of chemical reactions.

Lesson SequenceLesson Sequence• Lesson 1: Expressing and Measuring Reaction Lesson 1: Expressing and Measuring Reaction

RatesRates

• Lesson 2: Lesson 2: The Rate Law and Order of ReactionThe Rate Law and Order of Reaction

• Lesson 3: Theories of Reaction RatesLesson 3: Theories of Reaction Rates

• Lesson 4: Reaction Mechanisms and CatalystsLesson 4: Reaction Mechanisms and Catalysts

• Lesson 5: Lab InvestigationLesson 5: Lab Investigation

• Lesson 6: Lesson 6: ProjectProject

Curriculum ExpectationsCurriculum Expectations

D3.5D3.5 explain, using collision theory and explain, using collision theory and

potential energy diagrams, how factors potential energy diagrams, how factors

such as temperature, the surface area of such as temperature, the surface area of

the reactants, the nature of the reactants, the reactants, the nature of the reactants,

the addition of catalysts, and the the addition of catalysts, and the

Concentration of the solution control Concentration of the solution control

the rate of a chemical reactionthe rate of a chemical reaction

D2.8 D2.8 plan and conduct an inquiry to plan and conduct an inquiry to determinedetermine

how various factors (e.g., change in how various factors (e.g., change in temperature,temperature,

addition of a catalyst, increase in surface area addition of a catalyst, increase in surface area ofof

a solid reactant) affect the rate of a chemicala solid reactant) affect the rate of a chemical

reaction [IP, PR, AI]reaction [IP, PR, AI]

Advance PreparationAdvance Preparation

• Prerequisite for Prerequisite for Rate of ReactionRate of Reaction unit is knowledge unit is knowledge about about EnthalpyEnthalpy and and Heats of ReactionHeats of Reaction as well as as well as Hess’s LawHess’s Law and and Thermochemical EquationsThermochemical Equations. .

• Many lessons include Many lessons include computer simulationscomputer simulations, , therefore computers availability should be arranged therefore computers availability should be arranged in advance. in advance.

• For Lab Activities students should be asked to bring For Lab Activities students should be asked to bring lab coats, goggles and gloves. Video demonstration lab coats, goggles and gloves. Video demonstration require teacher to check up Internet and projector require teacher to check up Internet and projector function in the classroomfunction in the classroom

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

Teaching ApproachTeaching Approach ：：Expressing and Measuring Reaction Expressing and Measuring Reaction

RatesRates

Brainstorm ： slow and fast reactions, for example: rusting of metals, combustion.

Virtual Lab Demo: Mg and Fe reactions with HCl. http://www.infoplease.com/chemistry/simlab/singlehcl.html

Teaching Approach:Teaching Approach:The Rate Law and Order of The Rate Law and Order of

ReactionReaction

VideoVideo: concentration: concentration

and reaction ratesand reaction rates

Lab: Iodine-Starch ClockLab: Iodine-Starch Clock

to find empirically RR as function of initial concentration and formulate Rate Law equation:

Rate = k [A][A]mm[B][B]nn

k –rate constant; m, n –individual orders of reaction

Theories of Reaction RatesTheories of Reaction Rates

GizmoGizmo

Worksheet “Collision Worksheet “Collision Theory” and animationsTheory” and animations

Animation:

Factors affecting rate of reactions

Five factorsFive factors are affecting are affecting Rates of Reaction (Rates of Reaction (RRRR):):

• Nature of reactantNature of reactant

• ConcentrationConcentration

• Temperature Temperature

• Presence of a CatalystPresence of a Catalyst

• Surface areaSurface area

WHY?WHY?

Why?Why? It is explained by It is explained by Collision Theory:Collision Theory:

• The average The average kinetic energykinetic energy of particle is of particle is proportional to proportional to temperaturetemperature of sampleof sample

• Collisions Collisions of particlesof particles is is a musta must for for reaction to occurreaction to occur

• Only Only collision of particles with collision of particles with sufficient sufficient energyenergy leads to leads to successful reactionsuccessful reaction

• RRRR depends on depends on frequency frequency of collisions of collisions and the and the fraction of fraction of successfulsuccessful collisions collisions

Everything is because of Everything is because of ENERGYENERGY

That’s why reactions needs Activation Energy to occur

Not all particle have sufficient energy to provide successful reaction

Heating provides additional energy and more particle can be successful in collision

Teaching Approach:Teaching Approach:Reaction Mechanisms and Catalysts Reaction Mechanisms and Catalysts

actionaction

Animation:Animation: activity activity of of

homogeneous homogeneous catalystscatalysts

Molecularity Elementary step Rate law

1 A -> products rate = k [A]

2 A + A -> productsA + B -> products

rate = k [A]2

rate = k [A] [B]

3 A + A + A -> productsA + 2 B -> productsA + B + C -> products

rate = k [A]3

rate = k [A] [B]2

rate = k [A] [B] [C]

Jigsaw Activity on reaction mechanism and rate-determining problems solving

Teaching Approach:Teaching Approach:Inquiring LabInquiring Lab

In this lab activity students will examine In this lab activity students will examine some of some of the key factors that influence the rate of a the key factors that influence the rate of a reaction: reaction: – nature of reactantsnature of reactants– particle size particle size – temperature temperature – concentrationconcentration– catalystscatalystsStudents are given the lab materials and then Students are given the lab materials and then asked to design the procedure by themselves asked to design the procedure by themselves and predict the result.and predict the result.

Potential Student DifficultiesPotential Student Difficulties

• Students may mix up the stoichiometric Students may mix up the stoichiometric coefficients with reaction ordercoefficients with reaction order

• Finding the equation of line in Iodine Clock Finding the equation of line in Iodine Clock lablab

• Understanding that the frequency of Understanding that the frequency of collisions is not the function of temperaturecollisions is not the function of temperature

• Misconception of catalyst and enzymeMisconception of catalyst and enzyme

Solutions to Student DifficultiesSolutions to Student Difficulties• Show in the lab that Show in the lab that reaction orderreaction order is determined is determined empiricallyempirically and may be and may be non-integernon-integer number, number, differentiate with colors. Give some example of differentiate with colors. Give some example of non-integers orders.non-integers orders.

• Give the students Give the students general equation of a straight general equation of a straight lineline and review how it may be found from plot. and review how it may be found from plot.

• Contrast and show by animation that Contrast and show by animation that frequency of frequency of collisionscollisions does not does not increase significantly with increase significantly with temperature, but temperature, but average energyaverage energy of particle of particle doesdoes, , which is more important for reaction to occur.which is more important for reaction to occur.

• Asking students to brainstorm a list of what they Asking students to brainstorm a list of what they already know. Address that already know. Address that catalystscatalysts and and enzymesenzymes are regenerated unchanged at the end of a reaction, are regenerated unchanged at the end of a reaction, and they usually and they usually increase the rateincrease the rate of a reaction. of a reaction.

Applications and Societal Issues/ImplicationsApplications and Societal Issues/Implications

The project of “Bulletin” or “Thought Lab” is designed for applications and societal issues study.

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 and use electronic and print resources to research the substances to make a bulletin or an analysis report.

Applications and Societal Applications and Societal Issues/ImplicationsIssues/Implications

• Many Many reactions reactions that produce that produce usefuluseful compounds compounds proceed too slowlyproceed too slowly to be used in industries.to be used in industries.

• Chemists and engineers use Chemists and engineers use catalystscatalysts to speed upto speed up the reactions in the reactions in order to obtain products at a reasonable rate and under mild order to obtain products at a reasonable rate and under mild conditions. conditions.

• Biological catalystsBiological catalysts or or enzymesenzymes are are necessarynecessary to sustain life. to sustain life.

• Most Most drugs drugs and and vitaminsvitamins are involved in are involved in enzymeenzyme regulation. regulation.

• For some purposes For some purposes is beneficialis beneficial to slow downto slow down chemical reactions, chemical reactions, especially in food industry (food preservation reactants, storage in especially in food industry (food preservation reactants, storage in the cold conditions, in the liquid nitrogen, inert gases), inhibition of the cold conditions, in the liquid nitrogen, inert gases), inhibition of microorganisms growth, some surgical processes with body tissue microorganisms growth, some surgical processes with body tissue cooling, etc.cooling, etc.

• The rate of decay of a radioactive isotopes might also serve as a The rate of decay of a radioactive isotopes might also serve as a clock.clock.

• The project of “The project of “BulletinBulletin” or “” or “Thought LabThought Lab” can address some ” can address some applications and societal issues.applications and societal issues.

Differentiated AssessmentDifferentiated Assessment

• Assessment forfor learning Anecdotal notes during brainstorm, Q&A before and after Demo, checklist on answers on Anticipation Guide.

• Assessments asas learning Numerical problems solving, Questions and Answers, Worksheet answers checklist.

• Assessment ofof learning Self –assessment, Laboratory Report, Performance Checklist, peer evaluation in numeric problem solving, short quiz.

• The project of “Bulletin” can be alternated as a “thought lab”, a song, an essay, a diary entry, an animation or even a role play performance for multiple intelligence evaluation

AccommodationsAccommodations• Consult individual student Consult individual student IEPsIEPs for specific accommodation and modifications for specific accommodation and modifications

in teaching methodologiesin teaching methodologies

• When grouping students take into account availability of When grouping students take into account availability of peer helppeer help

• Help students with creation of Help students with creation of graphic organisersgraphic organisers

• Cooperate with Cooperate with special education providersspecial education providers about tests, assignment, etc. about tests, assignment, etc.• Permit ESL/ESD students to Permit ESL/ESD students to use translatorsuse translators and and extend timelinesextend timelines for them for them

• Record Record key wordskey words on the blackboard (or whiteboard) on the blackboard (or whiteboard)

• Provide Provide appropriate levelappropriate level resources for reading resources for reading

• Use more Use more visual aidsvisual aids

Safety ConsiderationsSafety Considerations

• Teacher review the safety rules before lab Teacher review the safety rules before lab and Students should have their lab coats, and Students should have their lab coats, goggles and gloves ready for use.goggles and gloves ready for use.

• As students will use computers to As students will use computers to complete virtual labs and research, it is complete virtual labs and research, it is important that teacher ensures students important that teacher ensures students using computer in a appropriate way. using computer in a appropriate way.