I find that collision theory is super intuitive, but its a bit difficult to teach without just explaining it straight out. Well after years of grappling with this challenge, I finally have it figured out. I found an easy inquiry activity that teaches collision theory.
As long as you tell your students to think about individual particles during this collision theory lab activity, it can certainly get the point across. All you’ll need are some glow sticks and some warm and cold water. Those glow sticks must come in at least two different sizes. I like to get the pendants and then the bracelets.
If you recall, the postulates of Collision Theory are that the reacting particles must collide with proper energy and orientation (effective collision) in order to have a chemical reaction. And there are a few ways we can increase the number of effective collisions:
- Make sure our components are actually going to react with each other.
- Increase the temperature.
- Increase pressure (if we’re working with a gas system)
- Increase concentration
- Increase surface area
- Add a catalyst
Of course, we can’t do all of these at once, nor can we do all of them with glow sticks. But this is a great activity to get the kids thinking about particles coming in contact with each other in order to react. You can have your students do this on their own, or you can do this as a demo. It works well either way, I’ve done both.
Trials for getting the particles to react:
The first thing I do is crack two glow sticks. I shake one and not the other. It’s a great way to get the ball rolling that the particles must come in contact in order to react. The kids can very easily figure this one out.
Then I take these two glow sticks and set one in hot water and one in cold water. While letting this sit for a minute, we crack two other glow sticks. These two glow sticks are of two different sizes. This has the kids realize that concentration is a factor in reaction rate. When there’s more stuff to react, more stuff reacts.
Then we head back to the warm and cold beakers. We make note of which glow stick is brighter. After our observations, we swap the two glow sticks. We give them another minute or so, and make observations. I have a really good time lapse of swapping the two glow sticks you can see in the gif below.
Pushing Students to Extend Their Thinking
After the kids learn about the factors that affect solubility, this is really not that difficult of a concept for my students to pick up on. And in my opinion that makes it a good inquiry activity for teaching collision theory. Many of my students struggle with this stuff. It’s hard for them to come up with rationale as to WHY a phenomena is happening. Partly I think this is because of the educational blip of 2020. But I also think that the phenomena teaching model is fairly new in science. Well not new. But more so, “freshly mainstream.” Some of us having been doing it for a while, but not all of our students have.
After the kids have figured out how concentration, contacts and temperature affect reaction rate we synthesize as a class. Then I make sure to ask them to hypothesize the other factors: surface area, pressure and use of a catalyst. I’ll then teach a mini lesson on collision theory and let them know whether they were right or wrong. I prefer to get it all out on the table, BUT you could hold off.
I like to use the Elephant’s Toothpaste lab activity to have them learn about catalysts and measure heat flow. We do this lab with my thermodynamics unit, but you very well could do this in your kinetics unit. Read more about the Elephant’s Toothpaste heat flow lab here.
