DFT was used to study the chemical transformation of [epsilon]-Co into its oxides and sulfides. Defect formation energies and migration barriers were calculated to determine the diffusion activation energies. Combining these results with experimental data allowed us to elucidate the dominant diffusion mechanisms in these systems. It was found that transformation from [epsilon]-Co to CoO occurs via an indirect-exchange mechanism, with Co atoms diffusing outwards and O atoms diffusing inwards. Once CoO forms, the mechanism changes; Co atoms diffuse outwards faster, forming a void inside. We looked at the Co-N, Co-F and Co-S systems to study the exciting indirectexchange mechanism in greater detail. Our observations helped us explain the mechanism lucidly, and predict that such a mechanism might be active in Co-N as well. We also studied an interesting anion-exchange reaction. We observed that Co and O atoms diffuse outwards, while S atoms hardly move, as CoO NPs transform to Co3S4.