What am I doing to help kids achieve?
How do I know when they are there?
What is the evidence?
Each year we work on specific heat of materials and the heat of fusion of ice. These are two labs that are typical for most chemistry classrooms. Most of the experiments involve a simple calorimetry experiment that uses a styrofoam cup and provides generally good results. There tend to be a couple of key ideas with all of these experiments. First, temperature is NOT the same as heat. Temperature is the average kinetic energy of a system and heat is the flow of energy from one system to another. Students (mine at least) get confused with this idea. Also, in both experiments, heat either flows out or into the water in the calorimeter. We know the specific heat, change in temperature and the mass of the water so we can solve for the heat. However, the heat had to come from somewhere, like a hot metal or go somewhere, like into the ice to change the phase. Common mistakes year after year have been confusing which mass is used in the heat equation. Typically, students confuse if they should use the mass of the water, ice or metal.
A couple of years ago I had the privilage of attending an American Chemical Society Conference in Dallas. The American Modeling Teachers Association did a presentation on modeling the idea of heat. First, they provide the analogy that heat is like money. Just as a person places money in different accounts, heat can be placed into different accounts and can be transferred from one account to another (it is represented as bar diagrams). It can be used to change temperature, thermal energy, or used to change the phase of a system. Also, heat can be stored in the "chemical energy" account which involves breaking and forming bonds. Students represent the heat in bar charts both before and after the change that occurs. An important step in the process is to identify the "system" (like ice, water or a piece of metal) and to see if heat is flowing in or out of the system and then to identify which account it would be in. Students also draw this in their energy diagrams. This method is different than traditional methods of teaching heat and the process I have shared here is the bare bones. The AMTA does a wonderful job of going into much more detail.
Here is the good news....since I have started using this method, I have had fewer students confuse the masses and the materials that are being heated and cooled in the equation for heat. The equation is definately symbolic and by physically drawing where the heat is stored, the flow of energy in or out of a system and where the energy ends in a bar diagram, students make a strong connection between the symbolic, the model and the lab that involves an extremely abstract concept such as "heat". Do all of my student "get" it? No. However, many more seem to be making the connections with this method than prior methods. If you also have students who struggle with this concept, I would encourage you to check out this method. I think it is a keeper....
Take a look at previous ChemEd X posts about Energy Bar Charts.
http://www.chemedx.org/blog/cross-discipline-discussions-energy (accessed 4/2/16)