Learners observe a sealed test tube containing a small amount of solid stearic acid. Under adult supervision, learners place the test tube into a beaker of hot water and observe the white stearic acid as it melts into a yellowish liquid. They then place the test tube into a beaker of ice water and observe as the stearic acid re-solidifies. Learners discover that changes in temperature can cause matter to change phases, but doesn't change the molecular structure. For safety reasons, this activity works best as a demonstration for younger audiences.