Question: What happens during an exothermic reaction?

A) Energy is absorbed, and the temperature decreases.
B) Energy is released, and the temperature increases.
C) No energy changes occur; everything stays the same.
D) The reaction only involves mixing substances.

Scenario: You conduct an experiment and mix NH4NO3\text{NH}_4\text{NO}_3NH4​NO3​ with water. You notice that the mixture feels cold to the touch, and the temperature drops.

Question: What do these changes indicate about the reaction? Do you think this is an endothermic reaction? Explain your reasoning.

A student conducts an experiment by combining solid ammonium nitrate (NH4NO3\text{NH}_4\text{NO}_3NH4​NO3​) with water in a calorimeter. After mixing, the temperature of the solution decreases significantly, and the student observes that the solution feels cold to the touch. In another experiment, the student mixes calcium chloride (CaCl2\text{CaCl}_2CaCl2​) with water, resulting in a noticeable temperature increase and the solution feeling warm.

Question:
Using the Law of Conservation of Energy, explain what is happening at the molecular level during these reactions. Identify which reaction is endothermic and which is exothermic, and describe the energy changes involved. How does the evidence from temperature changes and sensory observations (feeling cold or warm) support your conclusions? Additionally, discuss the implications of these types of reactions in real-world scenarios, such as in cold packs or heating pads.

What did I learn?

What was the most challenging part?

What can I improve next time?