# Question #af81a

Apr 2, 2017

This is the result of an $\text{endothermic reaction}$.

#### Explanation:

We may represent energy, or heat, by the symbol $\Delta$.

And thus we can represent an $\text{endothermic reaction}$ as:

$A + \Delta \rightarrow B$

The reaction absorbs heat from the surroundings.

On the other hand, for an $\text{exothermic reaction}$ we can write:

$A \rightarrow B + \Delta$

The reaction releases heat to the surroundings.

Typically, an ice pack contains solid ammonium nitrate in a capsule, surrounded by liquid water (or vice versa). The capsule is broken, the ammonium nitrate dissolves in the water and absorbs heat from the surroundings:

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

The ions are solvated by water, for which the energy required to break the strong ionic bonds is absorbed from the environment (i.e. the strain or sprain that you have managed to injure yourself with!).

As is typical, the making of bonds releases energy (i.e. $\text{exothermic}$), and the breaking of bonds requires energy ($\text{endothermic}$).