The Arizona STEM Acceleration Project
Modeling Kinetics:
An Inquiry activity for Kinetics in AP Chemistry
Modeling Kinetics
A 10-12 grade STEM lesson
Laura Winder
12/8/2023
Notes for teachers
This lesson and modeling activity is designed for use in an AP Chemistry course. Following the study of atomic and molecular structure and properties and chemical reactions, this lesson is meant as an introduction to kinetics, providing a framework for students to understand reaction order, mechanisms, and rate laws.
List of Materials:
*All pieces should be the same size and shape
Teacher Notes:
Because I used this as an introductory activity, we needed time (On a second day) to review and share group results as a class. This follow-up discussion occurred the next day, but did not take an entire class period. We went through each part, shared how each group’s results varied between reaction 1 and 2. We then discussed how to write the rate laws and answer the questions.
It was all new for the students so they had many questions about the application questions. However, I found that after using this as an introduction, my students grasped many of the concepts discussed later in the unit much more rapidly than in years I have taught this without the modeling introduction. It gave us a framework to fall back on and discuss as we referred to rate determining steps. reaction orders, and catalysts and their graphs.
Lab Instructions: I copy these as a class set of instructions for the students to follow. They record all their answers on the Student lab sheet below.
https://docs.google.com/document/d/1cWjzlNEFZ0KUIs6X6SR-4LqV7-8G8axXOBR4fHR1D5I/edit?usp=sharing
Student Lab Sheet:
https://docs.google.com/document/d/1RxviOAwrwugG1KdY0DWO0R8FHKWD8yty0NFAMLgQvOE/edit?usp=sharing
Standards
(From AP Chemistry Course and Exam Description, Unit 5 Chemical Kinetics)
Enduring Understanding TRA-3: Some reactions happen quickly, while others happen more slowly and depend on reactant concentrations and temperature.
Learning Objective TRA-3.B: Represent experimental data with a consistent rate law expression.
Essential Knowledge TRA-3.B.1 Experimental methods can be used to monitor the amounts of reactants and/or products of a reaction and to determine the rate of the reaction.
Essential Knowledge TRA-3.B.2 The rate law expresses the rate of a reaction as proportional to the concentration of each reactant raised to a power.
Essential Knowledge TRA-3.B.3 The power of each reactant in the rate law is the order of the reaction with respect to that reactant. The sum of the powers of the reactant concentrations in the rate law is the overall order of the reaction.
Essential Knowledge TRA-3.B.4 The proportionality constant in the rate law is called the rate constant. The value of this constant is temperature dependent and the units reflect the overall reaction order.
Essential Knowledge TRA-3.B.5 Comparing initial rates of a reaction is a method to determine the order with respect to each reactant.
STEM Ideas:
(From the Next Generation Science Standards)
HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
PS1.B: Chemical Reactions Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy.
Arizona Science Standard
HS.P1U1.3
Ask questions, plan, and carry out investigations to explore the cause and effect relationship between reaction rate factors.
Core Ideas for Using Science
U1: Scientists explain phenomena using evidence obtained from observations and/or scientific investigations. Evidence may lead to developing models and/or theories to make sense of phenomena. As new evidence is discovered, models and theories can be revised.
Objectives:
Students will be able to use models to explain how the collisions of particles affect the rate of a reaction.
Students observe and qualitatively distinguish between first order, second order, and zero order reactions.
Students will be able to explain how a slow step controls the overall rate of a reaction.
Students will be able to interpret graphs showing the potential energy of reactants and products and the activation energy of the transition state and relate the graphs to a corresponding reaction mechanism.
Intro/Driving Question/Opening
What factors control how fast a reaction will occur?
How can I predict how a change in concentration will affect the overall rate of a reaction?
Agenda
Day 1: (50 min class period)
Bellwork (3-5 minutes)
Ask students to think about and discuss: What is Kinetic Energy? Follow up with What do you think “Kinetics” might refer to? Elicit answers. Those who have had physics will probably say it is the study of motion, and may recall the study of position-time graphs. Tell them that today we’re studying the progress of a reaction, and that in chemistry we can monitor concentration as a way of keeping track of the position/progress of the reaction.
In-class Activity: (25-45 minutes)
N.B. If you have groups of 3, the Selector may also serve as the Mixer.
Role 1: Monitor - Keeps track of time and tells the group when to stop after the quota is complete.
Role 2: Mixer - Holds the bag and keeps mixing the particles.
Role 3: Selector - Blindfolded, reaches into the bag and selects the particle(s) for a potential reaction. Holds them up for the others to see. If the correct particle(s) for the reaction have been drawn, gives them to reactor. If incorrect particle(s) have been drawn, returns them to the bag and draws the next particle(s). Continues until the Monitor indicates that the quota is met.
Role 4: Reactor - Completes the reaction after the selector has drawn the correct particles. Place products on the table.
Pictures of the the activity in progress
Agenda
Day 2: (only 20 min of a class period)
Follow-up:
Share Class Data. Discuss questions students have about the graphs and data tables in the assignment.
This is a great time to throw out open ended situations and ask students to predict how the reaction would be affected or how they could model different reaction mechanisms not already included in the worksheet. For example, can they use this modeling activity to explain why trimolecular, 3rd order reactions are so rare? How fast would your activity go if you had to draw three different correct colors at the same time?
How does increasing the concentration of a reactant in a first step when the second step is rate-determining affect the overall rate of the reaction?
Move on to whatever lesson you typically teach at the beginning of the kinetics unit after completing this activity and the class discussion.
Assessment
This is an introductory activity and exploration for a unit on kinetics. I do not complete a summative assessment at this point in my unit. The worksheet and the student answers on the post activity questions serve as a formative assessment for this activity. Additionally the student questions and answers during the group discussion serve as a informal formative assessment for the teacher to determine what topics to spend more time on going forward in the unit.
Differentiation
Because this is an introductory activity, there should not be a need for remediation. Pair students who need additional support in groups capable of guiding them through the activity. The class discussion should help students make connections between the activity and the real chemical reactions the activity is meant to help describe.
Remediation
Extension/Enrichment
Students could be asked to model a new reaction set. Given a reaction mechanism, ask them to assign colors to the reactants and intermediates and determine which particles from which steps would be in the bag and must be draw randomly (slowing the reaction down and representing a slow step with a high activation energy) and which particles would be free to sit out and be assembled quickly.