Wednesday, April 5, 2017

Using Stop Motion Animation to show Reaction Mechanisms

Kinetics is a topic that I love to teach, but my students find it very difficult to understand. There are probably a variety of reasons for this, but one that I think contributes is that students struggle to think at the particle level in chemistry. If it's difficult to think about a sample of matter as being made of indescribably small and invisible particles, it is probably even more difficult to consider or propose the order of collisions that must occur in a successful chemical reaction. That is one of the challenges of teaching reaction mechanisms.

When the reaction     2 NO2 + F2 --> 2 NO2F    takes place, we know the reactants are 2 NO2 and F2. We know the products are 2 NO2F. We don't know, from the balanced equation, which particles must smash into which particles in order to change the reactants into products. We do know, though, that it is statistically unlikely that all three particles must crash into each other at once and instantly form products. Scientists propose a mechanism that outlines the order of the collisions that gets us from reactants to products.

I use a guided inquiry activity to tackle this topic every year. During my small group discussion with kids, I often need to use something to model the collisions that happen between the reactant molecules in the example reactions. Sometimes I use paper circles and sometimes circles I have drawn on the iPad. This year I grabbed small colored plastic cubes because they were handy. As I was talking with a student about the order of molecular collisions, it occurred to me that this would be a great occasion for a stop motion video, especially because, as a GIF, it could be watched over and over again until a student really understood the differences in the order of collisions of the same particles in two different mechanisms. 

I grabbed my iPad and took four quick pictures as the student and I talked through these collisions. Using the Stop Motion app, I created the GIF in fewer than five more minutes. Here it is:

It was very easy and can now be used as a tool to help students see the difference between two mechanisms. Next year I will try to incorporate making stop motion videos into the guided inquiry.

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