Question

What is the standard enthalpy of atomization?

Answer 1

The standard enthalpy of atomization, `DeltaH_"atom"^@`, for atoms is just for the process of converting however many `"mol"`s of the standard state (i.e. at `25^@ "C"` and `"1 atm"`) of the element needed to make `"1 mol"` of its gaseous form.

Thus the `DeltaH_"atom"^@` of `"Cl"_2(g)` to `"Cl"(g)` is for this reaction, for instance:

`1/2"Cl"_2(g) -> "Cl"(g)`

which is really half the enthalpy of breaking the `"Cl"-"Cl"` bond of `"1 mol"` of `"Cl"_2(g)` molecules, at `25^@ "C"` and `"1 atm"`.

For `"Cu"(s)`, which is a transition metal, its `DeltaH_"atom"^@` is based on the reaction:

`"Cu"(s) stackrel(Delta" ")(->) "Cu"(g)`

which in this case is really the enthalpy of sublimation for copper solid, at `25^@ "C"` and `"1 atm"`.