Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a pouch of water. When the pack is squeezed, the pouch breaks and the solid dissolves, lowering the temperature because of the endothermic reaction NH4NO3(s)+H2O(l)→NH4NO3(aq) ΔH= +25.7 kJ.
What is the final temperature in a squeezed cold pack that contains 43.0 g of NH4NO3 dissolved in 125 mL of water? Assume a specific heat of 4.18J/(g⋅∘C) for the solution, an initial temperature of 27.5 ∘C, and no heat transfer between the cold pack and the environment.
