For centuries, humans have put various items into their mittens and boots to help keep their fingers and toes warm when the weather outside was very cold. There are several different types of products advertised as “hand warmers” or “foot warmers.” Some of these products are designed to retain warmth from an exothermic chemical reaction or a physical change.

One type of hand warmer is composed of a tightly sealed and insulated packet within which there are two smaller packets. One packet holds a volume of water and the other packet holds a powdered solid. You twist or squeeze the packet, and then shake it a little to mix the materials. As the solid dissolves, it releases heat.


In the Initial Investigation, you will use a Temperature Probe to determine the temperature change of two substances as they dissolve in water. After completing the Initial Investigation, you will test several substances to determine which one can make the best hand warmer based on two factors: enthalpy of solution and cost.