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GeologyTutor
GeologyTutor, Geologist
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I am having trouble understanding endothermic and exothermic

Customer Question

I am having trouble understanding endothermic and exothermic reactions. I know the definitions of them but during my lab we added a small scoop of NH4NO3 to 5mL of water in a test tube. During this reaction the Initial temperature dropped from 19.7 degrees celsius to 13.0 degrees celsius. Do to the decrease in temperature change I classified this as exothermic. We also did the same thing for CaCl2, the Initial temperature also of 19.7 degrees celsius INCREASED to 37.3 degrees celsius; do to the increase in temperature I figured that it was endothermic since it absorbed heat.

Now I am asked to determine which one would be appropriate for a hot pack and a cold pack. In the question it tells me that a hot pack involves the release of heat and a cold pack becomes colder because it absorbs heat.

This information makes me believe that the hot pack would need NH4NO3 because this compound released heat; and that the cold pack would need CaCl2 because that compound absorbed heat.

What is making me second guess my answer is that all over the internet I am reading the complete opposite. Many other lab questions are saying that it is CaCl2 for a hotpack.

Maybe I just do not completely understand these terms and the reactions OR maybe I mixed up my results and wrote the temperature change in the wrong spot.

Any input would be great, Thanks.
Submitted: 4 years ago.
Category: Homework
Expert:  GeologyTutor replied 4 years ago.
Hello Customer,

The CaCl2 reaction is actually exothermic. You are getting an increase in temperature as it is dissolved so it is releasing heat into the environment as it dissolves. This is why CaCl2 is sometimes used to melt ice on roadways, so it would be the hot pack. NH4NO3 when added to water creates an endothermic reaction. You got a negative temperature change (the temperature went down) so it was absorbing heat (energy) from the water and this makes the water temperature go down. Because of this, NH4NO3 would be used in the cold pack.

I hope this makes sense. Let me know if you have other questions.
GeologyTutor, Geologist
Category: Homework
Satisfied Customers: 828
Experience: Professional Geologist, Tutored many high school and college students. Sciences and Religion
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Expert:  Chris M. replied 4 years ago.
THIS ANSWER IS LOCKED!

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