Most first aid “cold packs” are based on the endothermic dissolution of ammonium nitrate in water:

A particular cold pack contains 50.0 g of NH₄NO₃ and 125.0 g of water. When the pack is squeezed, the NH₄NO₃ dissolves in the water. If the pack and its contents are initially at 24.0°C, what is the lowest temperature that this bag could reach? (Assume that the ammonium nitrate solution has a specific heat of 4.25 J g^-1 K^-1, and that the heat capacity of the bag itself is small enough to be neglected.)

Transcribed Image Text:

NH4NO3(s) → NH4*(aq) + NO3(aq) ΔΗ° = 25.69 kJ