# Chemistry

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

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

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bobpursley
2. 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.

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bobpursley
3. 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".

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DrBob222

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