Chemical Reactions Unit Overview
I'm indebted to Nora Walsh, a chemistry teacher in southern Indiana who has comprehensive blog posts over on ChemEd XChange which helped me plan my own unit.
Small is better
This year, I decided to only focus on chemical reactions - their structure, interpretations, and types of reactions. In the past, I had included mol calculations as well. The intent was to help students make a direct link between the reaction ratios and material quantities, but that may have been too much of a stretch. Limiting my scope this year helped me stay laser focused on the key concepts so students could build deeper skill.
Our three learning objectives were:
- I can identify indicators of chemical change.
- I can balance chemical equations to satisfy the law of conservation of matter.
- I can classify types of chemical reactions based on the equation.
Demonstrations of learning
Because these were smaller, more discrete skills, I was able to have them do more targeted practice. My colleague, Melissa, pointed me to a fantastic resource to generate unlimited balancing and reaction ID questions for students to use on their own. Chemquiz.net has dozens of classes of questions you can generate for quick, immediate feedback activities. These shorter feedback cycles helped students catch misconceptions earlier and fix mistakes prior to the test.
I also updated my assignments to have some more written response. The work they submitted was more than skill demonstration - it was skill application. They did much more demonstration on their own, but it wasn't for a score in the book. I'm attempting to shift away from, "what work am I mising?" to "I'm struggling with this skill." It seems like it's taking longer this year to make the change than it has in the past and I'm hoping this particular structure will help.
Labs!
I've tried hard this year to make sure students have hands-on work whenever possible, especially as intro material. I want them to experience chemistry in action as part of the learning process, not as a result of the end of the unit.
I found a shared folder of mini-labs that I've modified into simple experiences for students. Each reaction demonstrates one of the five indicators of chemical change (temperature change, solid formation, gas formation, color change, or odor released) as well as modeling the five types of chemical reactions.
These labs have been sprinkled through the unit as qualitative demos. Students aren't expected to take data or do deep analysis - just observe and experience. These demos are available as reference materials on test days so they can construct responses with actual chemical examples.
Changes for next year
A notable crash and burn for this unit was my attempt to use a card activity to introduce and practice balancing. In principle, it looked great - students would work together to find coefficients for balanced equations. The cards provided a tactile interface and a way to discuss and debate the process.
In reality, the cards added overhead to an idea that totally took the focus away from the skill. They struggled to conceptualize multiple copies of the cards as represented by coefficients. They had a hard time sorting through the large bag of laminated slips to find the right chemical formulas in the first place. All in all, it was a bust.
If I were to redesign that activity, I would do fewer equations and have multiple copies of the same chemical. They could add units of chemical to find a balance and then abstract those duplicates into coefficients. Live and learn for next time suppose.
One lab in particular (the iodine clock) was too early for them. It relies on temperature and concentration differences, but they haven't learned about those yet. I think next time, I'll push that into our solution chem unit so they have a better connection between reaction rates (time) and amount of reactants.
I need to do a little bit more with exothermic and endothermic reaction qualities. These are fun to demo, especially when a reaction gets colder, but students struggled to explain why endothermic reactions, when they absorb heat, feel colder to the observer. Point of reference relationships weren't really a focus and that led to some misconceptions we'll need to address.
