Final answer:
Ammonium nitrate is used in instant ice packs and cold packs because its dissolution in water is an endothermic process that absorbs heat from the surroundings, resulting in a decrease in temperature.
Step-by-step explanation:
Ammonium nitrate is commonly used in instant ice packs and cold packs in hospitals because its dissolution in water is an endothermic process, meaning it absorbs heat from the surroundings. The temperature range for ammonium nitrate crystals and a pouch of water can vary depending on the specific conditions of the dissolution. However, an example from the information provided shows that when 3.21 g of solid NH4NO3 is dissolved in 50.0 g of water at 24.9 °C, the temperature decreases to 20.3 °C. This demonstrates the cooling effect of the dissolution process.