1. How are hot and cold packs constructed so that the reaction takes place only when needed? 2. Hypothesize two ways that you could change the amount of heat given off or absorbed in these packs.
1.They are constructed of a large pouch containing a dry chemical plus an inner pouch of water. The hot/cold pack is activated by breaking the seal on the pouch of water and shaking the pack vigorously. This action mixes the water
