A new linear relationship between absolute hardness and global activation energy of O-addition reaction to a series of aromatic hydrocarbons (benzene, naphthalene, phenanthrene, and pyrene) is presented. A total of seventeen O(3P)-addition reactions were evaluated. Thermal rate constants were calculated for each elementary reaction and used to estimate the total rate constants. This information was employed to obtain the global activation energy. A new linear relationship is shown and is estimated that it can be used within the RC-TST framework to predict relative rate constants for any reaction within an O-addition to PAH class from just absolute hardness values.