Chapter 9, Problem 9.78SP

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

${\text{NH}}_{\text{4}}{\text{NO}}_{\text{3}}\text{(s)}\stackrel{H_{2}O}{\to }{\text{NH}}_{\text{4}}{\text{NO}}_{\text{3}}\text{(aq)}$ $\Delta H$=+25.7kJ

What is the final temperature in a squeezed cold pack that contains 50.0 g of NH₄NO₃ dissolved in 125 mL of water? Assume a specific heat of 4.18 J/(g• °C) for the solution, an initial temperature of 25.0 °C, and no heat transfer between the cold pack and the environment.