Equations 10 and 11 quantitatively describe the O2 dependence on the rates of ZCuOCuZ formation, while the complex and likely non-elementary role of water molecules is captured within k6 (Scheme 1). While Scheme 1 and equations 5 -9 yield functional expressions that describe O2 activation kinetics, we note that this series of chemical transformations arises largely from chemical intuition and experimental observations. The unambiguous identification of the elementary steps that lead to ZCuOCuZ formation requires a combination of currently inaccessible synthetic methods and DFT-calculated reaction trajectories. Furthermore, DFT-calculated reaction pathways to quantitatively evaluate the free energy landscape of O2 activation may not yield meaningful results to interpret experimental data, because the values calculated are a strong function of the Al arrangement that influences the binuclear Cu configurations chosen. Even nominally "singlesite" Cu-CHA samples that contain only 6-MR isolated Al sites possess multiple types of Al-Al pair configurations in 8-MR windows that influence the energetics of binuclear Cu-oxo species formed.