T520: Exothermic and Endothermic Reactions – Hot and Cold Packs

Introduction

Commercial heat packs (containing iron and water, or supersaturated sodium acetate) and cold packs (various ammonium salts) can be used to show exo- and endothermicity.

Heat packs that contain iron and water packets:  Exposing the solution to air results in the oxidation of the iron (creates rust).  The oxidation of the iron is an exothermic process.

Heat packs that contain supersaturated sodium acetate:  These are reusable, the packs are boiled to dissolve sodium acetate.  Inside is a metal clicker, once the pack cools to room temperature, crystallization of sodium acetate (an exothermic process) is triggered by the clicker, which gives the sodium acetate a nucleation point.

Cold packs are presumably ammonium salts (judging by the stated contents).  The temperature change is apparently the heat of solution of the salt.

To Conduct Demonstration

1. • Set off heat packs and cold packs and pass them around the audience.

 Demo Time: 10 – 15  minutes

Safety 

The heat pack becomes quite hot.