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How does phosphorus(V) oxide react with water to form phosphoric acid?

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Phosphorus(V) oxide, also known as tetraphosphorus decaoxide ( $P_{4} O_{10}$ ), acts as the acid anhydride of orthophosphoric acid ( $H_{3} P O_{4}$ ).

When $P_{4} O_{10}$ is added to water, the reaction is highly exothermic, characterized by a hissing sound and the liberation of heat as the oxide reacts to form the acid. Due to its strong affinity for water, $P_{4} O_{10}$ is frequently utilized as a drying agent for gases and for removing water from various chemical compounds.1

The chemical equation for the reaction is:

$P_{4} O_{10} + 6 H_{2} O \to 4 H_{3} P O_{4}$

Industrially, large quantities of phosphorus(V) oxide are treated with water in this manner to produce phosphoric acid, which is essential for the production of phosphates used in fertilizers, detergents, and food applications.2