Final answer:
The best strategy for making a hot pack is to use an exothermic reaction that releases heat when a substance dissolves in water.
Step-by-step explanation:
When making a hot pack, the best strategy is to use a chemical reaction that is exothermic, meaning it releases heat. This can be achieved by using an exothermic reaction that occurs when a substance dissolves in water. For example, ammonium nitrate is commonly used in hot packs because its dissolution in water releases heat. The equation for the reaction is: NH₂NO₃ (s) + 25.7 kJ → NH₄ (aq) + NO₃ (aq). This heat released by the reaction helps to warm up the pack.