How can we choose the best chemicals to create a cold or hot pack?

➷ It would depend on whether they would create an endothermic reaction or exothermic. For a hot pack, the chemicals would need to release energy (heat). However, a cold pack would need chemicals that need to draw heat from the surroundings to produce a cool sensation.

➶ Hope This Helps You!

➶ Good Luck (:

➶ Have A Great Day ^-^

↬ ʜᴀɴɴᴀʜ ♡

alchemy hadn't scientific methods of study, appeal to mysticism and fantasy, the knowledge of chemistry and physics were modest at that time.

alchemy was - but as new rules were discovered it either changed into chemistry or it became "unscientific".