White dwarfs are made up of atoms in the plasma state; as thermonuclear reactions no longer occur in its nucleus, the star does not have any energy source that balances the gravitational collapse, so the white dwarf is compressing itself due to its own weight. The distance between the atoms within it decreases radically, so that the electrons have less space to move.
I believe that the delta h formation or enthalpy of
formation is only zero for pure elements. They are zero because they are the
most basic substances, that is you cannot form an element from an element.
Since Ozone is already a compound, a mixture of 2 oxygen O2 atoms, therefore
the δh∘<span>f is
not necessarily zero.</span>