Reusable Hand Warmer Crystallizes

Clear liquid turns solid and warm. Ask students to predict what will happen. Click metal disk and watch crystallization spread. Key idea: Supercooled sodium acetate crystallizes, releasing latent heat. Ask: Why does freezing/crystallizing make heat? Safety and cleanup: Use intact commercial pack. https://www.google.com/search?q=%22Reusable+Hand+Warmer+Crystallizes%22+science+demonstration+experiment