## Chemistry and Chemical Reactivity (9th Edition)

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.