CBSENEETJEEClass 11

What is enthalpy of atomisation?

Answer

Enthalpy of atomisation is the enthalpy change when one mole of a substance is completely broken into its gaseous atoms.

The working

Definition

It is the energy needed to convert one mole of a substance entirely into free gaseous atoms.

Symbol

It is denoted by Δ_a H° and is always positive because bonds must be broken.

For diatomic molecules

For a molecule like H₂, the enthalpy of atomisation equals the bond dissociation enthalpy of the H–H bond.

Example

H₂(g) → 2H(g) has Δ_a H° = 435.0 kJ/mol, the energy to split one mole of hydrogen molecules into atoms.

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