Hot Pack vs Cold Pack - Exothermic vs Endothermic Chemical Reactions

In this video I demonstrate a lab I do with my students to show them exothermic vs endothermic reactions. The exothermic reaction is calcium chloride mixed with water. It goes from cold to hot in seconds. The next reaction I did was ammonium nitrate mixed with water. This reactions also happens in seconds and get cold. Spontaneous temperature change, either hot or cold, is an indicator that a chemical reaction has occurred.