Eduardo hurts his knee during a basketball game. The trainer applies a cold pack, which gets cold after being squeezed. The next day, Eduardo’s friend Beth is going sledding. Beth buys some hand warmers and puts them into her gloves. All morning, her hands stay toasty warm. Required:
a. How do you think these devices work?
b. Where do you think the "cold" and the heat comes from?

How do you think these devices work?

Both devices follows the principle and endothermic and exothermic reactions.The cold pack is made up of two bags. The first bag contains water.And it is placed inside the second bag which contains NH4NO3 , and urea. Therefore, when the water bag is squeezed, the bag busted releasing the water  which dissolves  the surrounding  solid compounds. These compounds absolved heat energy in an endothermic reaction.

The components of hand warmers are  activated carbon, salt iron, water,,and cellulose.The Oxidation of iron when exposed to the air (oxygen)generated heat in an exothermic reaction to keep the hand warm.

Thus the cold results from the endothermic reaction as the solid compounds in cold packs absorbed water to break bonds to melts,and the hotness comes  from formation of new bonds(exothermic) as oxidation of Fe to form new compounds with other chemical occurs.

Explanation:

4d^55s^1 ( third choice)