# Why is an endothermic reaction cold?

Jul 4, 2018

$\text{Because it sux in heat from the surroundings...}$

#### Explanation:

$\text{Because it sux in heat from the surroundings...}$ (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...

$A + \Delta \rightarrow B$

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...

$N {H}_{4} N {O}_{3} \left(s\right) + \Delta \stackrel{{H}_{2} O}{\rightarrow} N {H}_{4}^{+} + N {O}_{3}^{-}$

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