Teaching the Concept of
Rates of Chemical Reactions
By: Tatiana Vrabie & Jiwei Li
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.
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Lesson Sequence
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Lesson 1: Expressing and Measuring Reaction
Rates
Lesson 2: The Rate Law and Order of Reaction
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Lesson 3: Theories of Reaction Rates
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Lesson 4: Reaction Mechanisms and Catalysts
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Lesson 5: Lab Investigation
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Lesson 6: Project
Curriculum Expectations
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
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
• Prerequisite for Rate of Reaction unit is knowledge
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•
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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
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/simla
b/singlehcl.html
Teaching Approach:
The Rate Law and Order of Reaction
Video: concentration
and reaction rates
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
Theories of Reaction Rates
Animation:
Factors affecting
rate of reactions
Gizmo
Worksheet “Collision
Theory” and animations
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:
• 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
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
Jigsaw Activity
on reaction mechanism
and rate-determining
problems solving
Molecularity
Elementary step
Rate law
1
A -> products
rate = k [A]
2
A + A -> products
A + B -> products
rate = k [A]2
rate = k [A] [B]
3
A + A + A -> products
A + 2 B -> products
A + B + C -> products
rate = k [A]3
rate = k [A] [B]2
rate = k [A] [B]
[C]
Animation: activity of
homogeneous catalysts
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
• 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
collisions does 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 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 Issues/Implications
• Many reactions that produce useful compounds proceed too slowly
to be used in industries.
• Chemists and engineers use catalysts to 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 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 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
• 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 of 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
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
• Teacher review the safety rules before lab and
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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.