Bromine molecules travel at about 200m/s in a vacuum. However, inside a tube of air, it take several minutes to travel even 40 cm. Why?

peasypod

The average speed of gas particles is temperature dependent (increases with the square root of T). However the mean free path (average distance a molecule travels before colliding with another) decreases with temperature and gas density. Hence even though the particles are moving rapidly, they collide with other particles and the diffusion speed may be very much smaller than the speed of the molecules themselves. Aug 30 06, 6:45 AM

elburcher

Think of Bromine traveling in a vacuum as your car on an open highway, you can zip along at 100 MPH no problem. Now think of Bromine traveling in "Air" as your car on a congested freeway, it slows down travel quite a bit because you have to interact with all the other cars. Bromine in air is much the same, it has to "push through"(for lack of a better term)all the "stuff" in air, while a vacuum is essentiely empty space. Aug 30 06, 8:31 AM