Chemical Thermodynamics (Nancy Delicana)

Overview

This self-assembly of magnetic pieces serves as a model that helps students visualize and understand how minimization of repulsive forces causes atoms or molecules to order themselves in nature. The general idea is to help students recognize that the interplay between enthalpy and entropy is a direct result of the system trying to lower its free energy. To illustrate these points, students will observe the self-assembly of floating round and square magnets inside different container size and shape and see how the pieces will order themselves to reach the lowest energy state.

CA Science Standards Grades 9-12

Physics

3d. Students know that the entropy is a quantity that measures the degree of order for a system and that entropy is larger for a more disordered system.

3e. Students know that most processes tend to decrease the order of the system over time, but in some processes, the order increases while the enthalpy decreases in order for the system to lower its overall energy.

Chemistry

7f. Students know how to use the Gibbs free energy equation to determine whether a reaction would be spontaneous.

I&E g. Recognize the usefulness and limitations of models and theories as scientific representations of reality.

Experimental Procedure

Materials:

· 70 pennies /group

· Penny challenge paper

· Either 1 pie tin plate or rectangular pan with a sliding edge for 3-4 students

· Water to cover bottom of containers

· 30 round floating magnetic for each group of 3-4 students

· 30 square floating magnetic pieces for each 3-4 students

· Paper towels

Penny Challenge

Working together in your group, place as many pennies, one at a time, into the three shapes- two squares and a circle and 100 pennies. Pennies must not overlap with each other and must be completely within the lines. How many pennies fit into each shape?

Floating Magnets

1. Put enough water in the containers to cover the bottom

2. Gather floating magnetic pieces of the same shape. you are given 30 circular and 30 square magnets in each kit. You will need 20 circular magnets for the round pan and for the square pan, and 20 square magnets for the square and for the round pan.

3. At each of the following steps, you will need to do the following: Gently shake the container to mix up the pieces but not hard enough to spill the water or flip over the pieces. you will have four experiments, Make sure you record observations every time.

· round floating magnetic pieces in a round pan

· square floating magnetic pieces in a round pan

· round floating magnetic pieces in a square pan

· square floating magnetic pieces in a square pan

4. One container at a time, place a single layer of magnetic pieces into water so that the magnetic dipoles are all facing the same direction, that is, all magnets should face the ceiling.

What structures are formed?_________________________________________________

5. For the square container, use the movable barrier to change the size of the container.

What happens to the structure?_______________________________________________

6. Flip over a few pieces so that not all the dipoles are aligned.

What structures are now formed?_____________________________________________

Challenge: What interesting structures can you make? ( arrow, stick figure, cross)?

References: http://voh.chem.ucla.edu/outreach.php3

California NanoSystems Institute, UCLA

Science Outreach Program