An instant cold pack usually consists of a rugged plastic bag with water and a soluble compound inside. The water is sealed in a fragile inner bag to keep it separated from the solid. When the cold pack is needed, it is squeezed to break open the inner container and bring the water and solid together. As the water and solid interact, heat is absorbed and temperature decreases.

Ammonium nitrate, NH4NO3, has been the solid most often used in instant cold packs. But, because it is much less hazardous, urea, (NH2)2CO, is replacing ammonium nitrate for this use. In this experiment, you will investigate the properties of urea and urea-containing cold packs.


In the Preliminary Activity, you will gain experience using a Temperature Probe as you determine the temperature change as a sample of urea dissolves in water.

After completing the Preliminary Activity, you will first use reference sources to find out more about cold packs, urea, and heat before you choose and investigate a researchable question dealing with urea or urea-containing cold packs.