The boiling point of a liquid depends on the external air pressure. In the Freezing by Boiling: Discrepant Event—ChemTopic™ Lab Activity, water is placed under vacuum, and as the boiling point decreases, the water boils, but during this endothermic process, the temperature decreases, and the water soon freezes! Available as part of the Solids and Liquids—ChemTopic™ Labs digital collection. Click the Price link for digital collection pricing.