Reusable Hand Warmer Crystallizes
Clear liquid turns solid and warm.
Teaching & key ideas
What you do: Click metal disk and watch crystallization spread.
What students see: Clear liquid turns solid and warm.
Why it works: Supercooled sodium acetate crystallizes, releasing latent heat.
Question to ask: Why does freezing/crystallizing make heat?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: Why does freezing/crystallizing make heat?