Teaching About Thermal Energy and Thermodynamics

Teaching Students the Laws of Thermodynamics by Making Ice Cream!

Sep 4, 2009

Thermodynamics, or the study of the relationship among thermal energy, heat, and work, is a basic tenet of physical science. Here is a fun way to teach this concept.

The Laws of Conservation are a prevailing theme in physical science, and the first law of thermodynamics reflects this in that energy cannot be created or destroyed, but can be transferred from one form to another. The second law of thermodynamics deals with this tricky concept of entropy. Although a rather complicated topic, the basic idea is that energy tends to become spread out or less concentrated over time. In other words, unless a system has an input of energy (in biological systems, for example, the sun) it will continue to become more disorganized (and thus the energy more spread out) over time.

Thermal Energy and Entropy and Ice Cream

Since heat is energy, heat flows from warm objects to cold objects, thus spreading out. An easy lab making ice cream demonstrates this property of energy transfer. A simple ice cream mixture can be placed in a bag, and that within a larger bag containing ice and salt.

The students will take turns shaking and kneading the bag of ice cream. The salt lowers the freezing point of the ice, so in order to melt the ice/salt mixture needs more heat, which it draws from the ice cream mixture. As the heat is transferred from the cream mixture into the salt water mixture, the ice cream begins to freeze.

Ingredients for Ice Cream Lab

Instructions for Ice Cream Lab

The mixture can be prepared the night before the lab will be conducted. Place the sugar, salt and milk in the top pan of a double boiler (difficult to make in a regular pan because the egg ends up cooking within the mixture if it gets too hot; can create a double boiler by resting a smaller pan inside a larger pan with the larger pan holding the water). Stir the egg yolks in, and cook the mixture over the boiling water until it becomes thick and bubbly around the edges.

Let the mixture cool, then stir in the vanilla and whipping cream. Divide the mixture into twelve small ziplock bags and seal well. Put three small bags into one gallon size ziplock bags and seal well. This can be easily transported to school.

Conducting the Ice Cream Lab With Students

Divide the students into groups of three. Give each group a large ziplock bag of ice cream mix (each with three small bags inside). Add salt and ice to each bag, and instruct students to take turns mixing the bags with their hands (kneading and shaking). Students will need to take turns, as their hands will get cold! Tell them to do this until it is thick enough to eat.

While they are mixing, tell them to think about what is causing the ice cream to freeze. Have students explain the process before allowing them to eat the ice cream. It may take them several times (and probably doing a little research) before they get it right. Once they answer correctly, have students remove the smaller bags, discard the large bag, and rinse the outside of the small bags well to remove the salt water mixture. Then give them spoons, and let them enjoy!

This lab is an enjoyable way to teach middle and high school aged students about thermodynamics, entropy and the Law of Conservation of Energy.

Feather, Ralph; McLaughlin, Charles; Thompson, Marilyn and Zike, Dinah. Physical Science with Earth Science. Columbus, OH: Glencoe/McGraw-Hill, 2006.

The copyright of the article Teaching About Thermal Energy and Thermodynamics in Lesson Plans & Materials is owned by Sara Wittenberg. Permission to republish Teaching About Thermal Energy and Thermodynamics in print or online must be granted by the author in writing.