Final answer:
The temperature of the pack increases as water mixes with lithium chloride due to the endothermic dissolution process that absorbs heat.
Step-by-step explanation:
When water mixes with lithium chloride (LiCl), the temperature of the pack increases. This endothermic reaction where water serves as the solvent involves the dissolution of LiCl, an ionic compound. Energy is required to separate the anions and cations of LiCl to overcome the lattice energy, causing the surrounding temperature to rise as the dissolution process absorbs heat.