Unit 9 Thermodynamics
I think this unit has my favorite demonstrations. I spread the demonstrations throughout this unit- allowing them to apply their knowledge as they learn it. The concepts are pretty straightforward, and this unit is especially easy for students who have a solid chemistry background due to all the overlap- specifically kinetic molecular theory and gas laws. I start this unit with a pHet simulation of gas properties to get students a visual of the gas particles, then go into the definitions of the three closely related concepts- heat, temperature, and energy. We move through gas laws quickly, tie back into fluids and make our first PV diagram with a Boyle’s Law lab, and spend the majority of the unit on PV diagrams.
One of the challenges of this unit is getting the terminology down- making sure students understand which variable, equation, and units go with heat, temperature, and internal energy. Heat energy and temperature they tend to accept really easily- I use melting an ice sculpture with a match as the example. Make sure students are comfortable with this concept before introducing internal energy- then connect it to heat- which is confusing because we use temperature to determine in on a PV diagram, but still- heat is the transfer, internal energy is the total, temperature is the average.
Demonstrations Thermodynamics
The demonstrations work well sprinkled throughout the unit- bringing it back to the flow of energy and giving anchors to the equations. They are also all pretty quick, so easy to do on the fly. While there are many demonstrations you can do for thermo- here are the ones I typically use:
Can Crush- heat a small amount of water in an aluminum can on a hot plate. Once steaming, use beaker tongs to quickly invert in a water bath- the air pressure ‘crushes’ the can- can explain using pressure or temp with volume.
Ice Melting Blocks- two different blocks with different thermal conductivities; the one that ‘feels colder’ will also be the one the ice melts faster on. Can purchase from science supply.
Water Works- heat round bottom flask- the bigger the better- that has been sealed with a stopper with a small glass tube through it. Same concepts as can crush, but water spurts through straw on inversion to water bath. It also takes a couple of seconds so I pretend I messed up then it’s a gorgeous water fountain.
The One with the Candle- a classic- light a candle in a pie tin surrounded by water (I just tape a tea candle down or birthday candles in playdough. Cover with a beaker and the flame goes out, then the water rises. Multi-part system!
Vacuum Bell Jar- put balloon, shaving cream, and a beaker of volatile alcohol that will boil at low pressures
Boyle’s Law Lab
Can you tell I stole the gas law lecture from my AP Chemistry curriculum? While a discussion of the individual gas laws isn’t necessary in the APP2 curriculum, I find it anchors the ideal gas law more and tells the application of the concepts will to go through the laws individually before the ideal gas law. During this lecture, we also need to teach the concept of the mole with respect to the variable N, Avogadro’s number, and Boltzman’s constant.
In the CED and Vernier lab books, they have a Boyle’s Law lab- one where students use pressure sensors to record pressure as they manually reduce the volume of a sample of a gas in a syringe, graphing the pressure vs. volume to create their first PV diagram (an isotherm). While I just use the Vernier lab from their chemistry curriculum, I added on using the force sensors to control the syringe- thus having them create a force pressure graph and get some practice with error- the slope should be the inverse of the area of the syringe.
I remember sitting in my AP Summer Institute being 100% lost while the instructor and rest of the class was working on a PV diagram activity, and learned right there that these are confusing and require lots of practice for students. Before we even start this lecture, we analyze the PV diagram from their lab. This lecture is gone through slowly, with many reassurances to students that we will practice these concepts.
Activity: Understanding PV Diagrams
I developed this card sort activity based off the activity I saw at APSI. Basically students are sorting these graphs on the 4 different factors we learn from them- work, internal energy, and heat. It takes about an hour to get through parts 1 and 2, and I typically assign part 3 as homework. I have the PV diagram cards printed and laminated, so students can annotate them with whiteboard markers. Students work on this in pairs or groups of 3, and have reported it really helped their understanding.
This is the new content for the ‘24-’25 school year. This ties in the thermal conductivity equation so much better, and provides a better basis of the why of the processes we study by explaining entropy and energy influences! Plus calorimetry can have some fun labs- I recommend doing a trial of 3 different ones- mix water, specific heat of unknown metal, and burning food or something!