|Why did my five gallon water bottle freeze before
my eyes when we brought it inside to stop it from
freezing. It formed star like ice crystals that
spread to the bottom in less than a minute! The
bottles had spent the night outside during a deep
freeze for this area. Two froze outside and two
froze in the house. How did that happen?
|Question Date: 2004-01-11|
This is a very difficult question to answer. I
discussed it with a few of my chemistry friends
and it seems the only close reason for this
situation is from super cooling. This situation
would be if the liquid came into contact with a
catalyst which caused a reaction making the liquid
freeze instantly. This catalyst could have been on
the wall of bottle and when the bottle was moved
it came into contact with the water. I hope this
Here is what happened:
When you cool down a
liquid, at a certain temperature it will freeze
(freezing temperature or freezing point). But
freezing implies the formation of crystals out of
the liquid phase. The molecules of a liquid will
not order themselves easily to form the solid
crystal, even if they have slowed down enough
(that is, even if the temperature has fallen below
the freezing point).
The appearance of a
crystal in the liquid phase, a process called
nucleation, always requires a solid surface with
some roughness where the first crystal seeds can
form. Once the "seeds" have formed, the formation
of the crystalline mass can happen amazingly fast.
Any process that brings a rough surface in contact
with the liquid can help the nucleation and
Scratching the internal walls
of the container often helps, stirring can
bringing into the liquid phase dust particles from
the air surrounding the liquid. Also intentionally
adding a very tiny crystal will produce the
A liquid in the state of water
in your bottle when you brought it in is said to
be "undercooled". Any dust particle falling on it
is generally enough to bring about the phenomenal
growth of ice crystals as you could observe.
Very nice crystals formed, weren't
There is also a very similar phenomenon
that happens when you dissolve too much solid into
a liquid solution. The solution can go to a state
of "supersaturation", and that means that it
contains more solute than it should according to
the solubility of the solid and the working
temperature. If in that solution you put a tiny
piece of the solid solute, most of the times you
will get the formation of large amount of crystals
in a very short time.
I hope you
understand now all about undercooling and
supersaturation, but if you need further
explanations, let me know.
You have observed a phenomenon called nucleation.
Sometimes, you can cool water below its freezing
point and it still will not freeze. However, in
such a condition, it is not stable and any little
help you provide (such as shaking the water when
you move it) is enough to make it freeze --- you
nucleate the freezing.
It is like having a
carefully balanced ball right at the top of a
small hill. Any little touch and the ball will roll.
The water in the jugs that didn't freeze was
probably super-cooled. In this case, they froze
not because you brought them inside but because
you physically moved them, and the water was ready
to crystallize at the slightest movement.
ice is a crystal, it needs some nucleus or other
imperfection to form. The molecules in the water
also have to move to aggregate themselves to form
ice crystals. If you have liquid water, that is
left perfectly still, it can be cooled down to
very low temperatures - well below the normal
freezing point - and yet stay liquid.
moment the water is jostled, however, some of the
molecules will find themselves aggregated into the
future crystal structure.
Once a crystal
forms, it causes other molecules to form the
crystal with it, so the crystals grow amazingly fast.
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