Hydration Enthalpy — Definition, Formula, Properties & Uses | AllChemicals | AllChemicals

Q: What is the formula for Hydration Enthalpy?

The formula or notation for Hydration Enthalpy is: ΔH_hyd = energy released when ion(g) → ion(aq); always negative (exothermic)

Formula / Notation	ΔH_hyd = energy released when ion(g) → ion(aq); always negative (exothermic)
Also Known As	Enthalpy of hydration, hydration energy, ΔH_hyd, ion-water interaction energy

What is Hydration Enthalpy?

The enthalpy change when one mole of gaseous ions are surrounded by water molecules to form aqueous ions. It is always negative (exothermic) because ion-dipole interactions form. Smaller, more highly charged ions have more negative hydration enthalpies.

Formula & Notation

ΔH_hyd = energy released when ion(g) → ion(aq); always negative (exothermic)

Other Names / Synonyms: Enthalpy of hydration, hydration energy, ΔH_hyd, ion-water interaction energy

Properties & Characteristics

Hydration enthalpy (enthalpy of hydration) is the heat released when one mole of gaseous ions is dissolved in water to form an infinitely dilute aqueous solution: M^n+(g) → M^n+(aq). It is always exothermic (strongly negative). Hydration enthalpy increases with higher ion charge and smaller ionic radius (greater charge density). Li⁺ has larger hydration enthalpy than Na⁺ (smaller, higher charge density despite lower charge). Balances lattice energy to determine solubility.

Uses & Applications

Hydration enthalpy is used with lattice energy in Born-Haber cycles to predict whether ionic compounds dissolve in water. If |ΔH_hyd| > |U_lattice|, dissolution is exothermic; if less, it is endothermic. Hydration enthalpy data guides selection of metal cations for specific applications (those with high hydration enthalpy have strongly bound water molecules).

Safety Information

Ions with very high hydration enthalpy release significant heat on dissolution (exothermic dissolution of CaCl₂, AlCl₃, FeCl₃). This can cause burns if dry salts are added to insufficient water. Solvation heat must be managed in large-scale dissolution operations.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Hydration Enthalpy

Formula ΔH_hyd = energy released when ion(g) → ion(aq); always negative (exothermic)

Index All "H" terms

Synonyms Enthalpy of hydration, hydration energy, ΔH_hyd, ion-water interaction energy

Frequently Asked Questions

What is Hydration Enthalpy?

The enthalpy change when one mole of gaseous ions are surrounded by water molecules to form aqueous ions. It is always negative (exothermic) because ion-dipole interactions form. Smaller, more highly charged ions have more negative hydration enthalpies.

What is Hydration Enthalpy used for?

Is Hydration Enthalpy hazardous?

What is the formula for Hydration Enthalpy?

More "H" Terms

Haber Process N₂ + 3H₂ ⇌ 2NH₃ | ΔH = −92 kJ/mol Hafnium Hf Half Cell Half Life Half-Cell E = E° − (RT/nF)lnQ Half-Life A(t) = A₀e^(−λt); t½ = ln2/λ Half-Reaction Halide X⁻ (e.g., F⁻, Cl⁻, Br⁻, I⁻) Halogen F₂, Cl₂, Br₂, I₂, At; Group 17; ns²np⁵ valence configuration Halogenation C-X + Cl₂/Br₂ (hv or AlCl₃) → C-X(halogen); EAS or radical pathway Halogens Hard Acid Hard acid: small, highly charged, low polarisability (e.g., H⁺, Mg²⁺, Al³⁺)

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