# diffusion confusion - (Jun/30/2008 )

hi

i was looking at some graphs i plotted just now and it looked weird. i was plotting diffusion rate of oxygen as a function of temperature, with this relationship plotted at different partial pressures of oxygen. what i got was, diffusion rate more affected by partial pressure gradient than temperature. is that right? does temperature generally have a weaker effect on diffusion rate than gradient of substance being diffused?

-mimi222-

yup! Of course depends on the temp range too.

-bob1-

QUOTE (bob1 @ Jun 30 2008, 06:11 PM)
yup! Of course depends on the temp range too.

i just found it weird because before i calculated diffusion rate, i first calculated the diffusion coefficient at different temperatures. the diffusion coefficient increased strongly and linearly with temperature, but the increase in diffusion rate is not as pronounced and the weak relationship between diffusion rate and temperature seems to diminish when oxygen partial pressure gradient drops. my temperature range is not very wide (from 35 to 7 degrees celsius), but why does this range affect the diffusion coefficient so severely and not the diffusion rate that much?

-mimi222-

What equation did you use, and if you used Fick's law, did you remember to convert your temepratures to Kelvin?

Wikipedia has relatively good articles here and here.

-bob1-

i used Fick's law and i did remember to convert the temperatures to Kelvin. the wiki pages are useful. thanks bob1

-mimi222-

Yes....

Diffusion by gradient is entropically driven...

Increasing temperature puts energy into the system... and THAT makes things move!

-doc_t-