Why can a safe sealed process become warmer or cooler?
A hand-warmer packet that gets hot when you snap it, or an instant cold-pack from the first-aid kit that turns icy when you squeeze it — both made from stuff that wasn't heated or chilled.
Talk about it
- Snap a hand-warmer packet and feel it get hot — then ask: nothing plugged it in, so where did the heat come from?
- Stir a spoon of baking soda into vinegar and touch the cup; it feels a little cooler. Where did the cup's warmth go?
- Both jars sat on the same shelf at the same temperature. Predict before mixing: will the cup stay the same, warm up, or cool down?