Brownian movement and diffusion

If there is a concentration difference in a body of water, there is a [net] movement of solute from high concentration to low concentration side, which in the end result in a uniform concentration everywhere the body of water.
But for an individual molecule, it doesn't necessarily move in that direction. It moves randomly as described as brownian movement.
As each solute and solvent molecule behave as brownian movement, eventually the concentration evens out.--> the same all over.

http://en.wikipedia.org/wiki/Brownian_movement
Brownian motion (named in honor of the botanist Robert Brown) is the random movement of particles suspended in a fluid.
http://en.wikipedia.org/wiki/Diffusion
Diffusion is the phenomenon of random motion causing a system to decay towards uniform conditions.

2007-07-30 08:56:58 補充：
would be better if you do your homework yourself!
shouldn't have helped you... regret...