Fick’s laws of diffusion describe the overall rate of this natural mixing process. These mathematical laws show that particles diffuse faster when the concentration difference is steep. Diffusion happens fastest in gases because gas particles move rapidly through empty space.
Graham’s law governs gas diffusion and shows that lighter molecules travel much faster. These lighter molecules have a higher speed than heavy ones at the same temperature. Diffusion in liquids occurs much more slowly because liquid molecules are packed tightly.
These close liquid molecules experience shifting intermolecular forces that resist free movement and mixing. Solid-state diffusion is the slowest form of this process because of rigid bonds. It happens when atoms slowly jump into empty spaces within a crystal lattice.
This solid diffusion requires very high temperatures to happen at a noticeable rate. The speed of diffusion depends heavily on the temperature of the medium. Heat increases the average kinetic energy and speed of all the particles involved.
This extra energy lets the molecules spread out and mix together much faster. A common student misconception is that particles stop moving when they reach equilibrium. In reality, the particles continue to move, but they move equally in all directions. Scientists call this stable state dynamic equilibrium because the movement never actually stops.