Question

What is Brownian motion and what does it have to do with diffusion? How is Brownian motion affected by molecular weight.

Answer 1

Brownian motion is a random motion of microscopic particles in a fluid as a result of continuous bombardment from molecules of the surrounding medium. These particles do not move any specific direction. For example movement of pollen grains in water.

Diffusion, on the other hand, is a movement of a substance from its higher concentration towards its lower concentration. Particles always move in a specific direction from high to low concentration. For example, osmosis is a special kind of diffusion.

Many factors affect Brownian motion like increased temperature, increased number of particles, small particle size, and low viscosity increase the rate of motion. Thus on increasing the molecular weight of particles the Brownian movement will decrease.