For this lesson students need several resources for the Magnesium Oxide Lab experiment.
- Bunsen burner
- metal tongs
- magnesium ribbon (about 4 cm)
- weighing boat
To begin the lesson I have students think back to the previous lesson where they were learning about what happens when two different substances with different temperatures are placed together. In particular I have them go back to their model paper and come up with a final model of what happens when equal amounts of 0 and 100 degree water are placed together. The goal of this section is to make sure that students are putting together the idea that in chemistry there are many phenomena that occur at the particle level which we cannot see so we must rely on what we can see at the macroscopic level to infer what is occurring with the molecules.
In this section of the lesson I introduce students to the idea of energy diagrams. This builds on their knowledge from the previous lesson where we discussed exothermic and endothermic reactions including how in exothermic reactions products have less energy; whereas in endothermic reactions products have more energy.
I present the information on the unit6 lecture 3- energy diagrams PowerPoint while students fill in their unit 6 lecture 3- energy diagrams student notes graphic organizer.
The lesson begins with looking at energy diagrams in terms of the reaction progress and energy of reactants and products. I also discuss the concept of Activation energy (slides 3-5). When I tell students about activation energy I use examples like "the spark needed to start the Bunsen burners" and "why you need to turn the ignition to get your car started"
I then discuss how there is a change in overall energy for a reaction ∆H which allows one to determine exothermic versus endothermic reactions (slides 6-7).
I then go over an example of an endothermic reaction (H2O (l) --> H2O (g)) and an exothermic reaction (N2 + 3H2 --> 2NH3) (slides 8-9). Here is a video of my reviewing the second example with students.
Here is a copy of one student's filled in notes.
In this section of the lesson I have students perform a lab activity to better understand energy diagrams and how energy changes during a chemical reaction.
Here is an example of a student's graded lab that received all points.
Some of the common mistakes that students make include performing the conversions to figure out the amount of energy given off by the reaction (#3), why the reaction needs to be heated to begin (#2), and how to do the proper sketch of the energy diagram (#4). For more details on this see my reflection below concerning student understanding in labs.