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Chemistry · Ch 5 — Thermodynamics

Enthalpy of Atomization

5.5(b)

Enthalpy of Atomization

Enthalpy of Atomization

Definition: The enthalpy of atomization is the enthalpy change when one mole of bonds is completely broken to obtain atoms in the gas phase.

Example — Dihydrogen:

H2(g)→2H(g);ΔaH⊖=435.0 kJ mol−1\text{H}_2(g) \rightarrow 2\text{H}(g); \quad \Delta_a H^\ominus = 435.0\ \text{kJ mol}^{-1}

H atoms are formed by breaking H–H bonds in dihydrogen. For diatomic molecules, the enthalpy of atomization is the same as the bond dissociation enthalpy.

Example — Methane:

CH4(g)→C(g)+4H(g);ΔaH⊖=1665 kJ mol−1\text{CH}_4(g) \rightarrow \text{C}(g) + 4\text{H}(g); \quad \Delta_a H^\ominus = 1665\ \text{kJ mol}^{-1}

Note that the products are only atoms of C and H in the gaseous phase.

Example — Sodium metal:

Na(s)→Na(g);ΔaH⊖=108.4 kJ mol−1\text{Na}(s) \rightarrow \text{Na}(g); \quad \Delta_a H^\ominus = 108.4\ \text{kJ mol}^{-1}

In this case, the enthalpy of atomization is the same as the enthalpy of sublimation. …

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