For ten points, identify this process by which molecules move from a higher concentration to a lower one.
In crystals, this process can occur via adatom hopping or quantum tunneling, which is an example of its "surface" variety observed in heterogenous catalysts. Uranium hexafluoride undergoes this process during enrichment. Its namesake coefficient is equal to the product of mean free path and velocity. Its flux is equal to the negative of the (*) concentration gradient in a law named after Fick, and this process is observed as water moves across a semipermeable membrane through osmosis. For ten points, identify this process by which molecules move from a higher concentration to a lower one.
In crystals, this process can occur via adatom hopping or quantum tunneling, which is an example of its "surface" variety observed in heterogenous catalysts.
diffusion