Teaching the concept of rates of chemical reactions by tatiana vrabie jiwei li
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Teaching the Concept of Rates of Chemical Reactions By: Tatiana Vrabie & Jiwei Li. Introduction to Reaction Rates.

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Teaching the Concept of Rates of Chemical Reactions By: Tatiana Vrabie & Jiwei Li

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Teaching the concept of rates of chemical reactions by tatiana vrabie jiwei li

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


Introduction to reaction rates

Introduction 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 sequence

Lesson Sequence

  • Lesson 1: Expressing and Measuring Reaction Rates

  • Lesson 2: The Rate Law and Order of Reaction

  • Lesson 3: Theories of Reaction Rates

  • Lesson 4: Reaction Mechanisms and Catalysts

  • Lesson 5: Lab Investigation

  • Lesson 6: Project


Curriculum expectations

Curriculum Expectations

D3.5 explain, using collision theory and

potentialenergy diagrams, how factors

such as temperature,the surface area of

the reactants, thenature of the reactants,

the addition of catalysts,and the

Concentrationof the solution control

the rate of a chemical reaction

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]


Advance preparation

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 approach expressing and measuring reaction rates

Teaching Approach:Expressing and Measuring Reaction Rates

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 the rate law and order of reaction

Teaching Approach:The Rate Law and Order of Reaction

Lab: Iodine-Starch Clock

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

Rate =k[A]m[B]n

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

Video: concentration

and reaction rates


Theories of reaction rates

Theories of Reaction Rates

Animation:

Factors affecting rate of reactions

Gizmo

Worksheet “Collision Theory” and animations


Five factors are affecting rates of reaction rr

Five factors are affecting Rates of Reaction (RR):

  • Nature of reactant

  • Concentration

  • Temperature

  • Presence of a Catalyst

  • Surface area

    WHY?


Why it is explained by collision theory

Why? It is explained by Collision Theory:

  • The average kinetic energy of particle is proportional to temperatureof 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


Everything is because of energy

Everything is because of ENERGY

Not all particle have sufficient energy to provide successful reaction

That’s why reactions needs Activation Energy to occur

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


Teaching approach reaction mechanisms and catalysts action

Teaching Approach:Reaction Mechanisms and Catalysts action

Jigsaw Activity on reaction mechanism and rate-determining problems solving

Animation: activity of

homogeneous catalysts


Teaching approach inquiring lab

Teaching Approach:Inquiring Lab

In this lab activity students will examine some of the key factors that influence the rate of a reaction:

  • nature of reactants

  • particle size

  • temperature

  • concentration

  • catalysts

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


Potential student difficulties

Potential Student Difficulties

Students may mix up the stoichiometric coefficients with reaction order

Finding the equation of line in Iodine Clock lab

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

Misconception of catalyst and enzyme


Solutions to student difficulties

Solutions to Student Difficulties

Show in the lab that reaction order is determined empirically and may be non-integer number, differentiate with colors. Give some example of non-integers orders.

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

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

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


Teaching the concept of rates of chemical reactions by tatiana vrabie jiwei li

Applications and SocietalIssues/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 issues implications

Applications and Societal Issues/Implications

  • Many reactions that produce useful compoundsproceed too slowly to be used in industries.

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

  • Biological catalysts or enzymes are necessary to sustain life.

  • Most drugs and vitamins are involved in enzyme regulation.

  • For some purposes is beneficialto 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 with body tissue cooling, etc.

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

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


Differentiated assessment

Differentiated Assessment

  • Assessment for learning

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

  • Assessments as learning

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

  • Assessment oflearning

    • 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


Accommodations

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

  • Cooperate with special education providers about tests, assignment, etc.

  • Permit ESL/ESD students to use translators and extend timelines for them

  • Record key words on the blackboard (or whiteboard)

  • Provide appropriate level resources for reading

  • Use more visual aids


Safety considerations

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 students using computer in a appropriate way.


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