RE: Diffusion coefficients

Steve Wrote:

>What I'm curious about is if there is any motivating force for diffusion 
of polarized >ion complexes aside from kinetic jiggling? Is there some sort 
of energy potential >which gets minimized as an ionic solution reaches 
equilibrium that would provide >motivating forces for diffusion? (recall 
that water molecules are polarized; that's >what makes it good at 
dissolving things)

The definition of equilibrium of a system is when the change in total Gibbs 
energy is zero : )  (I am a Chemical Engineer,  I had to mention Gibbs 
Energy).  Any ionic species will diffuse to reach equilibrium (hence 
cellular osmosis).  As the species approach equilibrium, the rate of 
diffusion might slow down if no outside force was acting upon it, but 
diffusion will still take place.

>BTW, feel free to launch into a discourse about the true nature of 
dissociated >salts in solution. It might be fun to read (well for some 

Lucky for everyone, I am not knowledgeable enough to talk about electrolyte 
chemistry.  Ask a Physical Chemistry professor.

>I wonder if there is anything we could make use of an electric field for 
in an >aquarium like maybe to pull nutrients around with? Maybe it would 
make the >plants grow better!

If you had pure water, nothing would happen seeing as you need charged 
particles for electron transference (current). : )  But, if you put the 
negatively charged plate of a large capacitor, with DC current, on the 
bottom (outside ; ) ) of the aquarium you could possibly provide enough of 
a field to attract the positively charged ions (Na+, K++, S++,Fe+,etc.) and 
improve the diffusion into the substrate.

Seriously though, heating coils would probably be better for diffusion, 
because they setup convection currents in the substrate which carry 
nutrient rich water and allow for diffusion to the roots of the plants.

>Steve (off on a tangential thread) ;-)

Really off on a tangent, but brought it home through heating coils.