Athletes often use instant cold packs to soothe injuries. Many of these packs use the dissociation of ammonium nitrate in water to create a cold-feeling compress. Is this reaction endothermic or exothermic?

A. Endothermic because the system ( the cold pack) gains heat as the surroundings lose heat***
B. Exothermic because the system ( the cold pack) gains heat as the surroundings lose heat
C. Endothermic because the system ( the cold pack) loses heat as the surroundings gain heat
D. Exothermic because the system ( the cold pack) loses heat as the surroundings gain heat

I definitely feel like the answer is endothermic, so that rules out answers B. and D.
But I feel like the answer is A. If I'm incorrect, please explain why

you are correct. "endo" thermic means energy is absorbed by the reaction.

the answers are a little misleading. Heat is not the only form of energy, there is energy in chemical bonding. If you read the word "heat" to mean "energy", then A is the only correct answer. Endothermic means accompanied by or requiring the absorption of energy (heat). If the surroundings lose heat, then the system (ie the reaction) gains (energy) heat.

To determine whether the reaction is endothermic or exothermic, you need to understand the concepts of energy transfer.

An endothermic reaction absorbs heat from its surroundings, causing a decrease in temperature in the surrounding environment. In contrast, an exothermic reaction releases heat to its surroundings, causing an increase in temperature in the surrounding environment.

In the case of the instant cold pack, specifically the dissociation of ammonium nitrate in water, we need to assess the temperature change of the system (the cold pack) and the surroundings.

When ammonium nitrate dissolves in water, it absorbs heat from the surroundings in order to break the bonds between the ions. This absorption of heat is an endothermic process, leading to a decrease in temperature in the surroundings. Therefore, the reaction is endothermic because the system (the cold pack) gains heat as the surroundings lose heat.

Correct Answer: A. Endothermic because the system (the cold pack) gains heat as the surroundings lose heat.

It isn't often that Bob Pursley and I disagree but on this question we do. There is no question that this is an endothermic reaction.

NH4NO3 + H2O + heat ==> NH4^+(aq) + NO3^-(aq) or
It takes energy to break the NH4-NO3 bond and that energy must come from somewhere. It comes from the water so the solution becomes colder; hence, the name "cold pack". Therefore, the correct answer is C. It is endothermic AND the solution loses heat as it becomes colder. If A were the correct answer clearly the solution would become warmer IF it gained heat and you would have a "hot pack" and not a "cold pack".

endothermic