# What is the standard enthalpy of atomization?

Jan 10, 2017

The standard enthalpy of atomization, $\Delta {H}_{\text{atom}}^{\circ}$, for atoms is just for the process of converting however many $\text{mol}$s of the standard state (i.e. at ${25}^{\circ} \text{C}$ and $\text{1 atm}$) of the element needed to make $\text{1 mol}$ of its gaseous form.

Thus the $\Delta {H}_{\text{atom}}^{\circ}$ of ${\text{Cl}}_{2} \left(g\right)$ to $\text{Cl} \left(g\right)$ is for this reaction, for instance:

$\frac{1}{2} \text{Cl"_2(g) -> "Cl} \left(g\right)$

which is really half the enthalpy of breaking the $\text{Cl"-"Cl}$ bond of $\text{1 mol}$ of ${\text{Cl}}_{2} \left(g\right)$ molecules, at ${25}^{\circ} \text{C}$ and $\text{1 atm}$.

For $\text{Cu} \left(s\right)$, which is a transition metal, its $\Delta {H}_{\text{atom}}^{\circ}$ is based on the reaction:

$\text{Cu"(s) stackrel(Delta" ")(->) "Cu} \left(g\right)$

which in this case is really the enthalpy of sublimation for copper solid, at ${25}^{\circ} \text{C}$ and $\text{1 atm}$.