Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: neilep on 14/09/2006 17:35:43

Title: Can water never freeze ?
Post by: neilep on 14/09/2006 17:35:43

I've often seen running water that is below 0 centigrade.

Is it possible to maintain  flowing water at such a speed that it never freezes ?...or is that just silly cos it would have to be flowing at such a stupid speed that it would evaporate ?

Is there a law to govern this ? (if there is..Please remember whom you are explaining it to !! [;)])

Thank you

Neil
xxxx

Men are the same as women, just inside out !

Title: Re: Can water never freeze ?
Post by: Karen W. on 14/09/2006 19:03:04

Yeah me too! Only I'm way worse then him so use real easy terms! Hey Neil thanks for the new topics.....Nice!!

Karen

Title: Re: Can water never freeze ?
Post by: lightarrow on 14/09/2006 21:35:20

If the water is very pure and it flows at temperatures not much less than zero in the more smooth way is possible, without perturbating it in any way, that is: avoiding vibrations, sounds, ice or dust particles, cosmic particles, electromagnetic radiations ecc., it actually hase no reason to solidify. I know, it seems a paradox.

But consider the fact that when water (or any other liquid) solidify, it realeses "latent heat of fusion", that is, the same amount of heat you had to give the ice to melt into water.

So, if water solidify, it releases that heat to...the same water that then... melts again the ice! It's not as simple as we could think! In a normal situation, that heat is actually dispersed in some way, for example is transferred to a larger amount of water or to the container's walls.

Liquids at temperatures lower than the melting point, vapours at Temp lower than the boiling point, solids at T higher then melting point, liquids at T higher than boiling point, are all possible, but they are in a state of non-equilibrium and these states are not very well understood because they are much more difficult to study.

In chemistry, physical chemistry and often in physics, most of the times it's said: "given this body in a state of equilibrium..."; yes, and what happens in a state of non-equilibrium, which is the most probable (and the most interesting) in a real situation? Everybody who studies physics or chemistry will make this question quite soon.

We always make a lot of assumption to simplify a real problem when we treat it scientifically. This is the strongest limitation of science and the reason to give science its real (limited) value. Let's remember that even science is just a product of human mind.
Having said this, we could understand more easily why science is so fascinating: something only originated from our minds can produce changes in the matter, in the real life! What really is magic?
This is.

Title: Re: Can water never freeze ?
Post by: krismi on 04/10/2006 03:15:26

Just to add something here.  The ionic strength of a solution (basically, how much salt is dissolved in the water) can have an effect on the the freezing point of water.  For example, seawater freezes at about -1.8 deg. C because of all the salts that are dissolved in it (it has a very high ionic stregth).  So, in addition to having physical momentum, natural water has dissolved salts, so its freezing point may be depressed below 0 deg. C.  This is only a different of 1.8 degrees, but it is still impressive what a difference a little salt can make!  And (as you've probably guessed) this is why we put salt on our front steps and roads.  See?  I told you it makes a noticable different!  (Certainly for me, for I slip and fall plenty withour ice!)

Title: Re: Can water never freeze ?
Post by: Xule on 09/10/2006 20:38:04

how much pressure the water is under could also have an effect on its freezing point

"Never tell the same lie twice."

Title: Re: Can water never freeze ?
Post by: Karen W. on 11/10/2006 06:27:23

Really the water pressure? How?

Karen

Title: Re: Can water never freeze ?
Post by: lightarrow on 11/10/2006 07:58:35

In the case of water, an increase in external pressure decreases the freezing/melting point, (and increases the boiling point, as all liquids). For example, no more 0°C and 100°C but -1°C and 101°C. This because water expands when freezes.

For a "normal" liquid, which contracts when it freezes ("normal" in the sense of much more usual; water behaviour is quite particular in this sense) increasing the external pressure increases the freezing/melting point.