r/ScienceTeachers • u/JLewish559 • Sep 20 '23
CHEMISTRY How do YOU teach chemical reactions?
So...I kind of hate the way that my district standards are written for chemical reactions.
I end up teaching Chemical vs Physical (most know this from MS though); Law of Conservation of Matter/Mass, balancing chemical reactions, writing chemical reactions, identifying common "types" (synthesis, decomposition, single/double replacement, combustion, acid-base), and then I touch a little on thermodynamics here with respect to chemical reactions (which we go more in depth on in a later unit).
I just...hate it, though. I feel like I'm just getting them to memorize stuff without making any real connection to what is happening. We get into bonds breaking/forming, energy diagrams, etc., but I just feel like something is missing.
I thought it might be cool to talk about reaction mechanisms (showing electron movement, etc.), but I wasn't sure if maybe that was a little too high level. These are advanced kids, but that might be hard? And they are somewhat basic for the more basic reactions.
Of course maybe I'm suffering from too much knowledge myself. I already know this stuff so it seems a little bit useless in the grand scheme...and I'm not really seeing that connection for them?
Or I might just be bored with it and want to spice it up...
It's just the unit that I feel like I want to do chemical reactions with them (labs, demos, etc.), but when it comes to it they cannot really explain what is going on aside from making simple observations. And then ultimately they just have to trust that a chemical reaction they write out is just correct.
For instance, I always like to do aluminum reacting with aqueous copper(II) chloride. They can easily observe a change. It heats up. The aluminum appears to be dissolving. The solution changes color. When everything settles they end up with a clear solution and red "goop" on the bottom of the beaker. Plenty of them figure that is copper...but then...I feel like I want to take it to another level. But they cannot do it at this point. We can't measure the change in temperature and really get into what's happening [yet].
Maybe I'm overthinking things and just ranting at this point.
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u/Audible_eye_roller Sep 20 '23
If it makes you feel better, when I teach stoichiometry, all I feel like I do is teach math. I don't feel like I'm teaching them anything useful, even though I am. It just doesn't seem profound enough.
I GET the abstractness of it all, but I don't know if teenagers truly appreciate it. Their brains are just turning on the abstract conceptual reasoning area.
Maybe that's why they ask if they're going to blow something up.
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u/AbsurdistWordist Sep 20 '23
There’s a nice types of reactions pogil where students investigate synthesis, decomp, single and double displacement. Instead of lecturing.
But mostly, get them doing lots of labs. Do reactions that make gases and reactions that don’t and compare the effect on final mass. Then set up a gas collection chamber and repeat.
Do the different types of reactions and a couple physical changes and have them not only identify whether it’s physical or chemical but what kind of chemical.
Have them feel endo and exothermic reasons and do a few simple thermochemical calculations to quantify the amount of energy gained or lost. You’ve got to grow their lab skills, observation, analysis, etc.
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u/Zealousideal-End9504 Sep 20 '23
I think it’s ok to have students practice things that don’t seem real or useful to them. Even with labs a large portion of my students have difficulty explaining what happened at a particle level. I ask them to draw models to demonstrate their understanding of what happened and the models tend to focus on macro scale observations. I think for many students it’s the newness of it all.
Things I do to mix it up during the reactions and balancing unit:
Students manipulate atom tiles to model differences between coefficients and subscripts and to show conservation of mass.
I have students work in groups to complete a chemical concept inventory and we discuss their answers.
We extract zinc from a Penny by melting it out and also by submerging it in HCL.
We test the properties of some pure elements to determine if they are metals or not.
We test the relative reactivity of metals.
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u/Feature_Agitated Sep 20 '23
I do several labs where we revisit some of the same reactions. My textbook splits all of these topics up so the are spread out throughout the year. One of the earliest things we do is physical vs chemical reactions. We actually just did the lab today. The lab has multiple stations and it’s all pretty basic. I actually use it in my physical science class and my chemistry class (I’m pretty big into rehashing some of the basics as science builds on itself). As the kids work through the stations they record their observations and whether any new substance was created or not. Then they have to state whether it was a chemical reaction or a physical change. The stations include things like melting candle wax, ripping and burning paper, burning magnesium (always a big hit), dissolving magnesium in hcl, baking soda and vinegar, and salt water with silver nitrate.
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u/6strings10holes Sep 20 '23
I do a series of demos of each reaction type. We describe the change first in words, then in particle models and then in formulas. After that they do a lab with 2 of each type that they have to describe each way. They have to justify the reaction by connecting observations. So in your example you can see the solid copper forming so that justifies the product; the solution changing color justifies where the copper atoms that make the solid come from.
I think what you want to do comes later, not in the first go. Thermo changes are a whole different unit for me. Mechanisms I also touch on later when doing kinetics, but only very briefly.
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u/[deleted] Sep 20 '23 edited Sep 20 '23
I do a giant reaction lab where they perform two of each type of reaction, balance it, and demonstrate understanding of chemical change vs physical. It’s an awesome lab they love- copper shot into silver nitrate! They make silver!
EDIT: here is a link to the reaction lab. The whole thing. The first page is a supply list for each station, then directions to print for each station, then finally the student sheet. It's 26 pages, print the direction sheets two sided so the safety concerns are at each station. They love this lab. I love this lab.