High-speed footage of water being poured on a watch glass containing dry phosphorus pentoxide. Phosphorus pentoxide is a powerful dehydrating agent, which reacts exothermically with water, giving off so much heat that some water is lost as steam. The reaction produces phosphoric acid. Phosphorus pentoxide is such a powerful dehydrating agent that it is used to remove water even from molecules to which the oxygen is tightly bound, such as amides, which feature a carbon-oxygen double bond.