Fick's second law....We do not talk about Fick's second law. That is mostly because your family members start looking at you weird and people stop inviting you to parties...Okay. That is just me being silly. The real deal with Fick's law is that Diffusion is also dependent on position inside the material as well as the concentration of the diffusing species at that location. After all, if two atoms that are identical switch places, no one will notice.