Chapter 9, Problem 9.82SP

Instant cold packs used to treat athletic injuries contain solid 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
$N{H}_{4}N{O}_3\left(s\right)\to N{H}_{4}N{O}_3\left(aq\right)$ $\Delta H=+25.\text{7 kJ}$
What is the final temperature in a squeezed cold pack that contains 50.0 g of $N{H}_{4}N{O}_3$ 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.