Which process describes mixing of gases by random molecular motion?

• A. Osmosis
• B. Diffusion
• C. Permeation
• D. Condensation

Answer: (B)

Diffusion is the process by which molecules spread from regions of higher concentration to regions of lower concentration because they move randomly due to thermal energy. In gases, this random motion is vigorous, so gas molecules continually wander and collide, gradually eliminating concentration differences and producing a uniform mixture. This spontaneous mixing by random molecular motion is exactly what diffusion describes, such as a scent diffusing through a room or a gas released into air spreading out. Osmosis involves solvent movement through a semipermeable membrane, not gas mixing in open space. Condensation is the gas-to-liquid phase change, and permeation refers to a substance passing through a barrier, not the general mixing of gases in a bulk.