Talk:Freezing

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 

this sounds like a textbook

  • That's because this is an encyclopedia.—GalacticExplorer 02:21, 30 June 2007 (UTC)
  • An encyclopedia and a textbook are different in the sense that an encyclopedia covers general knowledge but a textbook looks at a specific subject. I am completely sure, however, how one differentiates between them on the level of a single article/chapter. Perhaps the encyclopedia provides an overview of a subject in a single article that a textbook could examine in full and in more detail throughout the whole book. Still, I am not sure what is the point of the original comment. 62.31.116.126 16:12, 20 July 2007 (UTC)

Hot water vs. Cold water[edit]

what is the principle of freezing?

The Answer[edit]

Yes it does but why? some studies show it depends on the surroundings and evaporation. I'm not all that sure but it would be nice if someone added it to wikipedia.

Well, if you put a cup of cold water and a cup of boiling hot water in the freezer, the hot water would raise the temperature of the whole freezer; thus they would both freeze in the same time, but the cold water will take longer than if it were in the freezer by itself. Think outside the box 15:11, 29 September 2007 (UTC)

Its called the Mpemba Effect --KevinTraver 00:15, 16 November 2007 (UTC)

The real freezing point of water[edit]

In the absence of nucleators, water will only freeze (i.e. turn into a solid) at about -42 celsius (@ 1 atmosphere). Are people wrong to state that the freezing point is 0 celsius?

Yes they are wrong, but the melting point of water is 0 Celcius.---- Ben Best (talk) 19:50, 16 November 2007 (UTC)
No they are not wrong. The "real freezing point of water" at atmospheric pressure is 0 Celcius. Under special conditions one can achieve supercooling or even vitrification of water, but it doesn't have that much to do with freezing of water in its normal, thermodynamic, sense. --Cubbi (talk) 00:35, 18 November 2007 (UTC)
It is true that pure water in a liquid state below 0°C is in a metastable, non-equilibrium, supercooled condition. But that does not mean that ice will freeze near 0°C without nucleators. In the "normal", practical sense, absolutely pure water will not freeze much above −40°C. See the chapter "Principles of Ice Nucleation" by Gabor Vati in Biological Ice Nucleation and Its Applications. St. Paul, Minnesota: APS PRESS (The American Phytopathological Society). 1995. pp. 1–28. ISBN 0890541728.  Unknown parameter |coauthors= ignored (|author= suggested) (help). --Ben Best (talk) 01:01, 18 November 2007 (UTC)
I have replaced the About.com reference on the main page with the one I have cited above. I was the one who added the About.com reference in the first place, because the original text on the main page only gave a supercooling freezing point for very high pressures. I added the About.com reference knowing that it was misleading because it was readily available on the web, whereas the information in the nucleation book -- which is FAR more authoritative -- is not so easily verified by a browser. I am now going to go for accuracy rather than ease of confirmation by replacing the About.com reference. --Ben Best (talk) 05:20, 18 November 2007 (UTC)
I would not call that either normal or practical in any sense of the words. That's supercooling under very special conditions. --Cubbi (talk) 06:45, 18 November 2007 (UTC)
This is a matter of semantics. For water in the environment, it is "normal" for nucleators to be present, notably those of the bacterium Pseudomonas_syringae. That is why water can normally freeze at temperatures as high at −2°C (with a minumum of supercooling). SOME degree of supercooling is "normal" -- water NEVER freezes at 0°C except when it is in equilibrium with ice water. When no nucleators are present, supercooling to −40°C is "normal" -- although (as I said) the absence of nucleators is not "normal". To clarify these issues I have done more re-writing of the article, and I have added more journal references which should be more easily accessible than the book reference I gave. There are also links to other Wikipedia entries which give more support and background. --Ben Best (talk) 19:59, 18 November 2007 (UTC)
Better, but still, your references deal with water-based solutions within living organisms, mostly plants, which is not what most people think of when they say "water". This is even more narrow of a topic than supercooling in general. If one is to delve in such pecularities, why not bring in the freezing of water droplets in high altitude clouds and freezing of thin water films, Or how about the nanoscale ice bridges that form at room temperature between close surfaces? Do I *have* to look up references that say that water freezes at 0 C? --Cubbi (talk) 00:57, 19 November 2007 (UTC)
Your "common sense" view of the world is not scientifically informed. Water does not freeze at 0°C anywhere except in equilibrium with water ice. Water freezes at temperatures between −2°C and −8°C in streets, in ponds and in your freezer ONLY because of the presence of nucleators (particularly bacterial proteins) which are present almost everywhere in the environment. I challenge you to find an informed reference which says that PURE water (NO nucleators) will freeze much above −40°C. Read the references I have given. The journal CRYOBIOLOGY should be readily available in any biomedical library -- online (Elsevier), at minimum. --Ben Best (talk) 18:26, 19 November 2007 (UTC)
I don't mean to be, and don't like being, so harsh and confrontational. If nothing else, your comments deserve to be taken seriously because many readers are likely to have the same reaction as you do. The main article needs more words devoted to this matter of the dispelling the common misconception that water freezes at 0°C in the absence of nucleators. I notice that the Merck Index entry on water evades the question by only listing the melting point of ice, which is certainly 0°C. --Ben Best (talk) 22:21, 19 November 2007 (UTC)
I am fine with having what you've put up (it has a reliable source, after all, and it's interesting to know), my point is that it's a little too specific for the subject. If I find time to think of how to phrase this, I would write that freezing is a kinetics-controlled process, and although even a single degree of supercooling is unstable from thermodynamic point of view, freezing of bulk liquid is entropically demanding and, lacking all possible alternative pathways, most liquids overshoot their normal freezing point when their temperature is lowered. The mention of bacteria as the *main* such pathway strikes me as odd, I am used to dealing with pure water, which freezes on the irregularities of the container and on the gas/liquid interface. I have an issue with your idea of "dispelling the common misconception", because there isn't any. --Cubbi (talk) 04:52, 20 November 2007 (UTC)
Ben Best, I've downloaded that article you like so much. The opening paragraph is:
Water is the universal solvent of living organisms.
Pure water has an equilibrium freezing
point of 0°C, and solutes at the concentrations
that occur in the body fluids of living organisms
depress the equilibrium freezing point by not
more than a few degrees.
further down it says
The phenomenon in which aqueous solutions
remain in the liquid state when cooled below the
MP is known as supercooling. Solutions may
supercool to varying degrees before they spontaneously
freeze, and the temperature at which
spontaneous nucleation occurs is termed the
“supercooling point” (SCP) of the solution. The
supercooling capacity is the difference between
the MP and the SCP.
Some authors argue that since solutions may
be supercooled over a wide temperature range,
the term “supercooling point” makes no sense.
Instead, they prefer the term “temperature of
crystallization.” However, even crystallization
takes place over a wide temperature range; so
not much is achieved in logical clarity by the
substitution. A better term would be “nucleation
temperature.” The old term “supercooling
point” is well established and widely understood,
and this term is used in this review.
In addition, you've misrepresented the role of P. syringae completely:
Certain bacteria such as Pseudomonas syringae
possess very potent ice nucleators, which
they use to nucleate ice formation on the surface
of various fruits and plants. The freezing causes
injuries in the epithelia and makes the nutrients
in the underlying plant tissues available to the
bacteria
The bulk of the article deals with freezing of biological fluids found in the living tissues of plants and animals. What you insist on calling "real freezing point" is called "supecooling point" in your own reference. I am disappointed, this argument turned out to be a waste of time. --Cubbi (talk) 14:25, 20 November 2007 (UTC)
It is good that you read an authoritative article on the subject (Zachariassen KE, Kristiansen E (2000). "Ice nucleation and antinucleation in nature". CRYOBIOLOGY. 41 (4): 257–279. PMID 11222024.  -- which I will refer to as "the CRYOBIOLOGY article"), but I am afraid that you misinterpreted what you read. You have removed the thermal hysteresis page as a page in its own right (Thermal hysteresis ) and have made Thermal hysteresis into a redirect to the Antifreeze protein page: Antifreeze_protein#Thermal_Hysteresis. It is true that antifreeze proteins can increase thermal hystersis, but they are not the essential source or meaning of thermal hysteresis -- which is the fact that there is a difference between freezing temperature and melting temperature. The concept of hysteresis is applies to many phenomena, including temperature. You have added a reference to agar displaying this phenomenon in the introduction to the "Freezing" entry, which you have re-written. What does agar have to do with antifreeze protein? Here is what the CRYOBIOLOGY article says:
The separation of the melting point and the temperature of ice growth is termed thermal hysteresis,
and the temperature at which ice growth takes place is referred to as the "hysteresis freezing
point, (HFP), or just "freezing point". 
No mention of antifreeze proteins. Earlier it says
Since water usually will not freeze when cooled to the "freezing point," the term "freezing point"
is misleading and should be replaced by the more adequate terms "melting point" (MP) or "equilibrium
freezing point".
I call your attention especially to the first sentence of the section "FEATURES OF HOMOGENOUS NUCLEATION" on page 267 of the CRYOBIOLOGY article:
According to Vati (98), homogenous nucleation takes place at about −40°C, and the chance of
homogenous nucleation becomes negligible at a few degrees above this temperature. 
In the total absence of nucleators, water will not freeze much above −40°C, although the section does go on to say that this generalization does not apply to tiny water droplets, which can freeze as high as −15°C in the absence of nucleators if they are small enough. In the presence of the strongest nucleators water can freeze as high as between −1°C and −2°C, but no higher. Even in the presence of the strongest known nucleators water always supercools and will not freeze at 0°C, despite the fact that this is the "equilibrium freezing point". Even in the presence of the strongest known nucleators water displays thermal hysteresis. You have deleted from the article entirely the most authoritative book on the subject: Biological Ice Nucleation and Its Applications, which explains in great detail that Pseudomonas syringae produces the most powerful nucleating proteins known. If you can produce a reference giving a nucleating freezing temperature resulting from "irregularities of the container" I would be very surprised. You seem to be suggesting that "irregularities of the container" result in a nucleation temperature which is 0°C, a suggestion that simply makes no sense. No nucleator can possibly eliminate the thermal hysteresis of water, and even volcanic dust or other particles that often serve as nucleators in the environment are nowhere near as effective as the proteins from Pseudomonas syringae. Bacterial proteins are extremely widespread in the environment as contaminants and are most responsible for the fact that so little supercooling is normally observed in the freezing of water.
You have evidently put a lot of work and study into the editing of these pages, which has introduced new material, but you have also reduced the quality of information and introduced misinformation in the pages on Freezing, thermal hysteresis and Pseudomonas syringae. Hopefully, you are reasonable enough to now see the misconceptions you have introduced and restore correct information. I do not have much appetite for "revert wars", so I am not going to do any editing of these pages for several days, at least. I have some colleagues who I might invite to get involved in this matter if necessary (and if they take an interest in doing so), but they are on vacation until at least next week. --Ben Best (talk) 16:16, 21 November 2007 (UTC)


Big reply, let me see if I can break it down point by point

I explained the reason in the edit comment and its talk page. You are free to restore the page, after which I will put it up for AFD as non-notable and let others decide. After all, I am a biochemist, not a cryobiologist.
  • Even in the presence of the strongest known nucleators water displays thermal hysteresis
An ice crystal is a nucleator, commonly found in nature.
  • Bacterial proteins are extremely widespread in the environment as contaminants and are most responsible for the fact that so little supercooling is normally observed in the freezing of water
This is one point that I absolutely disagree with. Nature is not limited to the epitelium of the fruit that your favorite plant pathogen uses for food, and water is not limited to the run-off from the infected orchads. Think about it, if it really *was* as ubiquitious as you say, none of the commercial P.syringae-based snow-making machines and ice-forming additives would have ever worked! --Cubbi (talk) 20:13, 21 November 2007 (UTC)

Сhemical Freeze[edit]

carbonic acid, sulphuric acid and water.

95.59.73.185 (talk) 07:36, 2 July 2016 (UTC)Chursin Dmitry