Final answer:
The statement about hot packs utilizing sodium acetate crystallization for warmth is true; they contain a supersaturated solution of sodium acetate that releases heat when crystallized by activating a metal trigger.
Step-by-step explanation:
The statement that hot packs used by skiers and climbers are based on the crystallization of sodium acetate from a highly concentrated solution is indeed true. These packs contain a supersaturated solution of sodium acetate (NaC₂H₃O₂). When a small metal trigger within the pack is activated, usually by bending or 'clicking' it, it initiates a mechanical shockwave that causes the sodium acetate to precipitate out of solution. The process of crystallization generates heat, which is then used to warm the hands or body. This thermochemical reaction is an exothermic process, meaning it releases heat as the substance transitions from a dissolved to a solid state.
Commercial heat packs available at drugstores typically operate on this principle. In contrast, cold packs often use a different chemical reaction that involves an endothermic process, such as the dissolution of ammonium nitrate (NH₄NO₃), which absorbs heat from the surroundings to provide a cooling effect.