Diffusion Mystery: How Does Perfume Spread in a Room?

When a bottle of perfume is opened, the smell spreads around the room through a process called diffusion. This is because perfume molecules evaporate and the vapor disperses, moving from an area of high concentration (near the opened bottle) to areas of lower concentration until the smell is perceptible throughout the room.

The spreading is a result of the random and constant motion of gas molecules, as articulated in Graham's Law, which describes how gases diffuse and effuse given their kinetic properties. The mean free path relates to the average distance a molecule travels before colliding with another molecule, and it helps to explain how molecules can travel through air to reach places like our olfactory cells, allowing us to detect scents.

Furthermore, this dispersion of perfume molecules results in increased entropy, representing a more disordered state, which explains why the molecules do not spontaneously return to the bottle.