Exploring Collision Theory

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Objective

SWBAT derive the key aspects of the collision theory of reactions from observations on a computer simulation.

Big Idea

For chemical reactions to occur, particles must collide with precise alignment and enough kinetic energy.

Background

This was the second day out of our Spring Break.  The week prior to break was our PARCC testing, and schedules were hectic.  Students were still absent from taking additional days off for break on Monday.  Uncertain what I would be facing in terms of attendance on this day, I scaled this lesson back.

For a direct instruction lesson, the ExploreLearning Gizmo on Collision Theory is fantastic.  It demonstrates the basics of collision theory, and then has experiments for students to run testing out the effects of changing surface area, temperature, concentration and catalysts.

HS-PS1-5 reads: 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.  In our first year of NGSS, we did this PE in a short period of time using the Gizmo as a model (SP2) to examine the behavior or particles at a level unobservable to a student.  The latter part explores the Scale, Proportion and Quantity Cross Cutting Concept that some systems can only be studied indirectly as they are too small to observe directly.

I decided I wanted this to run a little different this year.  I wanted to introduce the basics of collision theory to my students, and then have them plan an inquiry investigation using an aspect of the collision theory to affect the rate of a chemical reaction.  Fellow Master Teacher Eric Girard and I collaborated on that lesson, which can be found here.

This finds an abbreviated version of the Gizmo worksheet, modified down to the needs of the lesson.  Due to the poor attendance on Monday, I am also providing students time to work on the Mid-Term review to get caught up.

 

Introduction

5 minutes

When the period begins, I welcome students back, and ask how the first day from break went for them.  After engaging in some small talk about getting back into the flow of the semester, I explain that we will begin our new unit today, focusing on the speed of chemical reactions.

I ask for student ideas of when we want reactions to happen faster than normal.  Some responses include:

  • Medicines
  • Cooking food
  • Dying/straightening hair
  • Charging batteries (a new response this year- thank you Generation Selfie!)

I then ask when we might want reactions to be slower.  Students struggle on this some, as they are so addicted to the fast pace of culture.

  • Food spoiling
  • Car rusting

I remind students that reactions involve atoms re-arranging, and that since we can't see the atoms in action, we will be using our computer simulations to help us visualize it.  I ask students to go log into the computers, and that I will bring them the guide sheet when they are logged in.

Simulation

25 minutes

As students are logging into the computers, I pass out the Collision Theory Exploration document.  While the computers are coming up, I encourage students to answer the Prior Knowledge questions.  I have noticed this year that many students skip these questions, and it hurts their ability to connect to what the lesson is about.

While students are opening the Gizmo, I distribute the blue, green and orange markers/colored pencils to the tables.  These are needed for the students to complete the Warm-Up and sketch the reactants and products.

This student was typical of the classes.  They don't indicate what switched in their description.  For next time, I will make students write a generic chemical equation for this, and indicate that it is a single replacement reaction to help review the types of reactions and connect our content throughout the semester.

As students continued to play, they had a hard time identifying the three requirements for reactions to happen.  However, they were excellent at identifying the macro-scale factors that can affect the reaction rate.

This student did better, recognizing that the reactants has to be moving, but not connecting speed with temperature.  She also identified that the collision was essential to the reaction.

Identifying many issues with full recognition of the three components of collision theory (collision with proper alignment and enough kinetic energy), I decided to give a short lecture the following day on the collision theory to firm up the gaps after the Gizmo.

When students finished this part of the Gizmo, they had time to explore further and play around on the simulation, or to work on completing their Mid-Term Review, depending on individual need.

Mid-Term Review Completion

25 minutes

While students worked on the Semester 2 Midterm Review I circulated the room to help them remember concepts, direct them back into their notes, and catch up about their Spring Break.  The review helped get students back in the swing of the semester, and identify gaps in retention.  I use this to point out concepts to students that they will need to still know for units (chemical reactions, the mole) and to help them practice recall. 

Some students also needed to complete either the multiple choice or short answer portions of the Stoichiometry unit test from before break, so I also put students into study groups and helped them review during this time.