Why is an endothermic reaction cold?

1 Answer
anor277
Jul 4, 2018

#"Because it sux in heat from the surroundings..."#

Explanation:

#"Because it sux in heat from the surroundings..."# (I could not use the regular spelling, as the forum school-m'am software would not permit it, and thank God for that because I am sure we would have all blushed).

We would write an endothermic reaction from #A# to #B# in this way...

#A+Delta rarr B#

Of course the heat has to come from somewhere...and it comes from the surroundings. Have you ever used a cold-pack as a first aid device? These are usually solid mixes of ammonium nitrate (and other salts) with a blister of water... When you use it you BREAK the blister, and the water reacts with the ammonium salt.

And because such reaction is entropy rather than enthalpy-driven, heat is taken from the surroundings...

#NH_4NO_3(s)+Deltastackrel(H_2O)rarrNH_4^(+) + NO_3^(-)#

And such a reaction can be used to provide topical relief to swelling or a strain...

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