Build Thermal Energy Device Practice Test

A class is designing an instant hot pack using magnesium sulfate (Epsom salt) or calcium chloride. The pack must (1) start heating only when activated, (2) be easy to activate with one squeeze, and (3) keep chemicals separated from the user. Which construction plan best meets all three requirements?​

A reusable hand warmer uses a sealed pouch of supersaturated sodium acetate solution and a small metal “click disk” inside. When the disk is flexed, crystals begin forming and the pouch warms to about 50°C. Which statement best describes the thermal energy change that makes the pouch warm?