Answer
See answer below.
Work Step by Step
Enthalpies of formation (kJ/mol)
$O(g): 249.170, O_2(g): 0, O_3(g): 142.67$
Oxygen's standard state is $O_2(g)$.
Formation of oxygen atoms from $O_2(g)$ is endothermic since the former has a higher enthalpy of formation than the latter.
To create 1 mol of ozone from $O_2(g)$ 142.67 kJ are required.
