Teaching the Concept of Rates of Chemical Reactions By: Tatiana Vrabie & Jiwei Li. Introduction to Reaction Rates.
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Teaching the Concept ofRates of Chemical ReactionsBy: Tatiana Vrabie & Jiwei Li
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.
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]
Brainstorm：slow and fast reactions, for example: rusting of metals, combustion.
Virtual Lab Demo: Mg and Fe reactions with HCl.
Lab: Iodine-Starch Clock
to find empirically RR as function of initial concentration and formulate Rate Law equation:
k –rate constant; m, n –individual orders of reaction
and reaction rates
Factors affecting rate of reactions
Worksheet “Collision Theory” and animations
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
Jigsaw Activity on reaction mechanism and rate-determining problems solving
Animation: activity of
In this lab activity students will examine some of the key factors that influence the rate of a reaction:
Students are given the lab materials and then asked to design the procedure by themselves and predict the result.
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
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.
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.