States of Matter - Diffusion

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.

According to the Kinetic Molecular Theory, particles in liquids and gases are in constant, random motion. In gases, particles travel in straight lines until they collide with other particles or the walls of the container.

The rate of diffusion is inversely proportional to the square root of the molar mass ($M_r$) of the particles. This principle is known as Graham's Law of Diffusion.

Temperature significantly affects the rate of diffusion. As temperature increases, particles gain more kinetic energy ($E_k$), leading to higher velocities ($v$) and more frequent collisions, thus increasing the diffusion rate.

Diffusion occurs most rapidly in gases due to large intermolecular spaces and high velocities, slower in liquids because particles are closer together with stronger intermolecular forces, and is negligible in solids.

In a closed system involving the reaction of two gases like $NH_3$ and $HCl$, a white ring of ammonium chloride ($NH_4Cl$) forms closer to the $HCl$ source because $NH_3$ has a lower molecular mass and diffuses faster.