[kfa]

Why is the rate of diffusion of particles in solids and liquids are lower than that in gases?

[Yggdrasil]

Does diffusion occur in solids?  Anyway, in liquids, particles are more densely packed.  This means that collisions between molecules will occur more frequently.  Since collisions tend to randomize the direction that the molecule is traveling, a higher the collision rate makes it harder for particles to travel larger distances.

[wilson]

Does diffusion occur in solids?  Anyway, in liquids, particles are more densely packed.  This means that collisions between molecules will occur more frequently.  Since collisions tend to randomize the direction that the molecule is traveling, a higher the collision rate makes it harder for particles to travel larger distances.

I suppose diffusion can occur in gels (e.g. Agar). Minute, that's it.
Instead of focussing so much on the spaces between particles, I think that the speed at which the particles are moving can also be taken into account.

When particles of a gas move at a rapid rate, they can travel larger distances as well, hence diffusing faster. Does this make sense?

[Borek]

Diffusion occurs in solids. It is just slow.

http://www.google.com/search?q=diffusion+coefficients+in+solids