Diffusion in Liquids
What is diffusion in liquids and
how does it happen?
Diffusion is mainly gases property.
The kinetic theory predicts the ability of two or more
gases to intermix or dissolve in each other in all
Diffusion is shown also by liquids but much less.
Gases and liquids are fluids, that is they can flow
easily, the gases more than the liquids. We can
imagine that fluids have as much of occupied space
as empty space (or "holes") into their volume.
Diffusion of a gas (or liquid) into a liquid
to the occupation of these empty spaces. depending
upon the liquid viscosity, temperature and other
Thanks for asking NEWTON!
(Dr, Mabel Rodrigues)
If you had a cup full of slippery rubber balls, and you were always
shaking it enough so the balls were slightly bouncing around,
occasionally the single red ball in the bunch would slip between a
momentarily large gap between two other balls.
Then it would have a new home.
Eventually, this red-marked ball will get to every place in the cup.
The balls represent atoms, which are often both elastic (rubbery) and
The bouncing is just about like heat.
The "atoms slipping past each other" is diffusion.
This slipping happens rarely and slowly in solids.
You can imagine that only one atom at a time is lucky enough to slip to a
So the solid mostly keeps holding its shape.
Slipping happens very often and fairly fast in liquids.
Significant percentages of the atoms in a liquid are slipping past each
other at any given time,
so the whole mass can deform smoothly in response to small pushes.
In this conceptualization, what holds these balls close together is
gravity and the cup.
With this kind of confinement, it is hard to imagine a sharp distinction
between solid, liquid, and gas-like states.
To clearly imagine solid, liquid, and gas, you should imagine that each
ball has a "magnet" in it,
attracting all the neighboring balls with a modest pulling force that does
not reach very far.
So the liquid holds itself together in the presence of a certain amount of
It can exist without gravity or the cup.
If the bouncing is much weaker, the balls settle closer together and form
a rigid stack of balls, which is much like solids do.
If the bouncing is much stronger, the balls mostly escape far from each
and just bounce off walls and each other sporadically. That is like a gas.
If you viewed an exhibit having a big mass of such balls,
if there was enough bouncing to be "liquid", the mass would look rather
No wonder that things eventually move around in a liquid.
If the bouncing was weak enough to simulate the solid state, the mass
would look jittery but
your eye could tell that it was mostly staying in place.
Then it might be interesting to watch and wait for occasional "hops" and
You would even notice a few "holes", spots with a ball missing,
migrating around a little and not getting filled in.
The scientific word for these holes is "vacancies".
Vacancies are created and destroyed mostly at the surfaces of the mass.
In the solid they slip around faster than atoms, so they help diffusion.
Most substances expand when they melt.
You can think of it as a solid being invaded by about 10% "holes", enough
to be lubricated to liquid-like motion.
You can see that diffusion will happen in all three states, at
appropriately differing rates.
Diffusion is a property by which gases or liquids mix spontaneously
because of the random motion of their particles. I hope that this helps.
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Update: June 2012