Differentiated Exploration of Collision Theory
Lesson 6 of 17
Objective: SWBAT explain how adding a catalyst or manipulating the temperature, surface area or concentration affects the rate of reaction according to the Collision Theory of Chemical Reactions.
This lesson is the immediate follow-up to the Alka-Seltzer investigations. Since each student group chose their own reaction condition for the investigation, they have become experts at the effects of either:
- Surface Area
What we did not investigate yet were catalysts. Since students still have some gaps in their expertise, this activity looks to fill in some of the gaps.
For this, I assigned the students an aspect of chemical reactions they did not work with in lab. Students had an opportunity to work on a second aspect for extra credit if they had time. To bring things together, the students work on a review after doing the modified Exploration with the Gizmo. I allowed students to collaborate with each other for the portions they were unfamiliar with.
I made the choice to perform this as a jigsaw to help students focus, and not spend time on a reaction factor that they had spent four days on. In hindsight, I should have ensured that students investigated ALL of the factors they did not do in their investigation to complete their picture of the factors that can change the rate of a reaction.
This lesson is aligned to the following 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.
- Science and Engineering Practice 2: Develop and use models.
- Systems and System Models Cross Cutting Concept: Middle School
- Systems and System Models Cross Cutting Concept: High School
Opener and Instructions
When students enter the room they are eager to know what they got on their posters. I explain that it takes time to carefully grade 50+ posters, but that I will have everything graded by the following Monday.
I ask students to raise their hands if they tested the effect of temperature in lab. Then I survey for those who did surface area, and lastly concentration(amount of water). I ask if anyone is certain of how each change affected the reactions in our investigations.
When students have shrugged, or complained "How could we if we only tested one thing?" I explain today's procedure. Students will use the computers to explore one change that is different than their lab investigation. If they have time to complete a second exploration, I will count it as extra credit.
Students will have 30 minutes on the computers, at which time they need to get off the computers and work on the review. They may need to talk to members of other groups during the review to get the information they are missing.
I dismiss students to the computers in lab so that they can begin to log in.
While students are logging into the computers, I pass out the Collision Theory- Jigsaw documents. These are slightly modified versions of the ExploreLearning Exploration sheet for the Collision Theory Gizmo. I seed the room heavily with the catalyst, concentration, and surface area sheets as so many students had outstanding experimental results on changing temperature that I am not worried about them understanding it.
As students are working, I am circulating the room checking in with them, and helping them understand the controls in the Gizmo.
The most common refrain to students is to do the steps in order and read everything. I find students get confused because they have been taught to skim and scan so much that they apply it to everything.
The students working on concentration need a little assistance, as we have not covered molarities this year, so I explain the units to each group, and have them observe what happens when they change the molarity. This is a student example of a completed concentration paper:
One of the issues I have with this is students end up treating the seconds like decimals, so their mean half-life is inaccurate. However, it isn't inaccurate enough to take away from the learning about reaction rates, so I don't fret too much so long as they have an accurate trend in their data. For next year, I would likely have them convert the times to seconds and then just find the mean of the seconds.
This student collected data on the changes in surface area. Students had difficulty with this concept, mainly because they don't necessarily understand what surface area is. I found out afterwards that our Geometry classes didn't teach that concept for another month. In the previous school year, when this was our last unit, it coincided with the Geometry instruction.
The students working on the concentration of a catalyst had the hardest task, as they had to figure out what it was about the catalyst that was speeding the reaction. I made many of the groups watch it 3-4 times both with and without the catalyst so they could contrast what they were seeing.
When students finish, they log out of the computer and transition to the front of the classroom to work on the summative review.
Reaction Rate Review
When students come to the front of the room, they get the Collision Theory Review and begin working on it. This review is meant to help them build some connections:
- Temperature affects the kinetic energy of molecules
- Concentration and surface area affect the number of collisions between molecules
- Catalysts help align the collisions
As well as those connections to the collision theory, there is a basic pattern that should emerge also:
- Increasing any factor increases the rate of the reaction
- Decreasing any factor decreases the rate of the reaction.
Students will do the factors they are familiar with from the Alka-Seltzer investigation and the Gizmo jigsaw first, then seek out classmates to help fill in the gaps. Some students prefer to ask me, so I will only seed them on the way to figuring it out, whereas they can get a full explanation from a classmate.
I want them interacting and explaining to each other, hence my not offering full explanations to students. I am hoping that in explaining the concepts to each other, they will better cement the ideas for themselves.
The problem with jigsaws is that if the students don't have the correct information, they can mislead each other. As you can see below, the student was backwards on the effects of concentration and confused it with affecting the kinetic energy of a sample.
This student did better, excepting the idea that catalysts slow reactions
Unfortunately, there was not time for a final check in before dismissing students. Therefore, the Reaction Rate Quiz the following day didn't go as smoothly as hoped for.