Diffusion

Vacuum Gas Pinhole

Vacuum Gas Pinhole

Diffusion vs. Effusion Diffusion - The tendency of the molecules of a given substance to move from regions of higher concentration to regions of lower concentration Examples: A scent spreading throughout a room or people entering a theme park Effusion - The process by which gas particles under pressure pass through a tiny hole Examples: Air slowly leaking out of a tire or helium leaking out of a balloon

Graham’s Law Diffusion –Spreading of gas molecules throughout a container until evenly distributed. e.g. perfume bottle spillsEffusion –Passing of gas molecules through a tiny opening in a container e.g. helium gas leaks out of a balloon Courtesy Christy Johannesson

Effusion Particles in regions of high concentration spread out into regions of low concentration, filling the space available to them.

Weather & Air Pressure HIGH pressure = good weather LOW LOW pressure = bad weather

Weather and Diffusion Map showing tornado risk in the U.S. Highest High LOW Air Pressure HIGH Air Pressure

Hurricane Bonnie, Atlantic Ocean STS-47

Hurricane Wilma Hurricane Wilma October 19, kPa in eye

NET NET MOVEMENT To use Graham’s Law, both gases must be at same temperature. diffusion diffusion: particle movement from high to low concentration effusion effusion: diffusion of gas particles through an opening For gases, rates of diffusion & effusion obey Graham’s law: more massive = slow; less massive = fast