Enthalpy of formation

[Adrienne_4F]

What other molecules besides O2 and N2 have o enthalpy of formation?

[Emmaraf 1K]

Any element in its most stable state has an enthalpy of formation of 0. If you look at a periodic table which has states of matter labelled, the element in that state of matter has an enthalpy of formation of 0 except for diatomics which must have 2 atoms present at their most stable state of matter to be in their most stable state.

[Henry Dudley 1G]

Just to add to the previous response, only elements, compounds, molecules, etc. that are not in their most stable states have enthalpies of formation that are not 0.