Re: [Phys-l] sudden Vacuum freezing

[John Denker <jsd@av8n.com>]

On 05/08/2007 09:22 AM, Chuck Britton wrote:

> It was not frozen when I later popped the cap and took a swig - then 
> I noticed a tiny white spot on the surface of the (liquid) beer. As I 
> watched - the spot grew slowly and then BAM - the whole bottle became 
> a beer slushy. 


I'll bet it expanded quite a bit during the process.

There is a bunch of interesting chemistry and physics going
on in this system.

1) In the unopened bottle, there is a four-way equilibrium
involving
  a) gaseous CO2 in the head space
  b) CO2 dissolved as such in the liquid
  c) item (b) reacted to form aqueous H2CO3
  d) item (c) ionized to form H(+) and HCO3(-)

Items (b), (c), and (d) contribute to lowering the freezing
point in the usual colligative way.

When you take the lid off, the equilibrium shifts by a
huge amount, and all of the aforementioned items exit the
scene (on various timescales).

2) There is a classic, beautiful scaling argument that explains
why there is a barrier against nucleation of bubbles in
such situations.  Surface tension is energy per unit area
and tends to crush the bubble.  Pressure is energy per unit
volume and tends to expand the bubble.  Do the scaling and
discover that small bubbles get crushed to nothingness,
while not-so-small bubbles grow.  A bubble in a crack,
such as provided by a boiling chip, has less surface per
unit volume and can grow more easily;  this is called
inhomogeneous nucleation.

A Pilsner glass is engineered to cultivate inhomogeneous
nucleation at special sites near the bottom.

   (You didn't think I was going to pass up a chance
   to make a scaling argument, did you? :-)