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How does sulfuric acid behave when dissolved in water?

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When sulfuric acid is dissolved in water, it exhibits several distinct behaviors:

Exothermic Reaction: Anhydrous sulfuric acid mixes with water in all proportions through a highly exothermic reaction, meaning it releases a significant amount of heat. Because of this, it is essential to add the acid to water slowly while stirring to distribute the heat and prevent dangerous, explosive spattering.1
Dissociation: As a strong mineral acid, it ionizes completely in water to form hydronium ions ( $H_{3} O^{+}$ ) and hydrogen sulfate ions ( $H S O_{4}^{-}$ ). In dilute solutions, the hydrogen sulfate ions further dissociate into additional hydronium ions and sulfate ions ( $S O_{4}^{2 -}$ ). Because it can donate two hydrogen ions per molecule in sequence, it is classified as a diprotic acid.2
Hygroscopic Nature: Concentrated sulfuric acid is highly hygroscopic, meaning it readily draws moisture from the air. When exposed to the atmosphere, it absorbs water vapor, which dilutes the acid and increases its total volume.2