An athlete gets hurt on the football field, and the trainer brings the athlete a cold pack. Before he places the cold pack on the athlete’s leg, he breaks the vial inside the pack. Instantly, the pack gets cold. This is an example of what type of reaction?

A Endothermic.

explanation

During an endothermic reaction, the temperature of the substance drops, or gets colder. When the trainer broke the vial in the ice pack, he caused an endothermic reaction.