What happens inside an ice pack? The chemistry of cooling an ice pack

Emanuele Mortarotti in
12 April 2023

What happens inside an ice pack? Why do the ingredients inside reach a temperature below zero in just seconds? Everything can be explained with a chemical reaction.

disposable ice packs

Welcome back to the Dispotech blog!

We have often spoken about instant ice, about the duration of the cold sensation generated by ice packs and their composition.

But do you know what happens inside an ice pack? Why do the ingredients inside reach a sub-zero temperature in just seconds? Science comes to our aid – in particular, a chemical reaction.

Let’s find out more with the support of an article read on simplechemconcepts.com.

Ice packs are commonly used items that we all have at home - whether professional or ‘emergency’ objects made with frozen vegetables that we might grab from the freezer. The benefits of ice can be used to relieve a particularly aggressive headache, to reduce a swollen ankle after a bad sprain. In a word, having an ice pack at home - instant, in gel or improvised - is without a doubt a good idea.

Instant ice is sold on the market packaged in disposable bags that are activated by a chemical reaction: what we are talking about is an endothermic reaction. It is because of this chemical phenomenon that, for example, instant ice packs do not need to stay in the freezer: a little gesture is all it takes to have a cold bag for more than 20 minutes.

But now let’s have a closer look with the help of chemistry.

The principle that ammonium salts such as ammonium nitrate dissolve in water absorbing heat is at the core of the ice packs we find at a pharmacy and in specialty shops: this is the most natural example of an endothermic reaction.

Instant cold packs usually contain a small amount of ammonium nitrate or ammonium chloride, both of which are separated from the water by a thin shell. The moment you press the centre of the bag with your fingers, the two shells break. The salts dissolve in the water and the endothermic reaction causes the heat released from the contact between salts and water to be absorbed by the bag.

This final step gives the cooling sensation we feel when an ice pack is placed on the skin or a painful area.

Did you know the chemistry behind the workings of an instant ice pack? Contact Dispotech.