This heat pack contains a super saturated solution of water and sodium acetate. Snapping the metal disc creates an exothermic chain reaction, causing the solution to crystallize. Heat packs can be recharged back to the liquid state by boiling in water for 10-15 minutes and allowing to slowly cool. Excellent for teaching about chemical reactions and introducing thermodynamics.
• Comes with a Teacher’s Guide
• 100 x 100 mm (4 x 4 in)