Hot water freezes faster than cold water

[HydrogenBond]

In chemistry water is normally represented as a bent molecule with an almost tetrahedral shape with two hydrogen atoms and two non bonded electron pairs.


What they have found is the two non bonded electrons pairs sort of merge between where they thought the two non bonded electrons were, much closer to the oxygen atom.



When water forms ice then the tetrahedral sort of returns. But when water is hydrogen bonded to some proteins, the water is triangular. The bent shape allows the hydrogen to share the electrons on another water.

[koji8123]

Originally Posted by Moontanman

Evaporation is important but you have left out a big part of the puzzle. Heating water drives out all the dissolved gasses. Dissolved gasses act like antifreeze driving the freezing point down making it harder to freeze water that contains the gasses. Heated water not only cools fast it also freezes closer to the freezing point of pure water.

right that's why if you were to boil the water, evaporating most of the minerals in the water to get it closer to H20.

[alexander]

right that's why if you were to boil the water, evaporating most of the minerals in the water to get it closer to H20.

methinks it works the other way around, since mineral's melting and evaporation points are much, much higher then that of water, it is water that evaporates, and minerals remain (hence why they make distilled water by collecting and condensing the vapor)

simple experiment, really, take some water, and add salt to it, mix it till there is no more salt, now set the pot down on a burner, and boil the water out, what are you left with, in the pot?

[Dutchdivco]

My 1st post, after intro'ing myself. Water is a fascinating stuff, no doubt.Read its the only substance that expands, when heated or cooled. (Not counting things like milk, which is largely water).Anyone know of an explanation or theory as to why it expands when frozen? Jim

[Moontanman]

Originally Posted by Dutchdivco

My 1st post, after intro'ing myself. Water is a fascinating stuff, no doubt.Read its the only substance that expands, when heated or cooled. (Not counting things like milk, which is largely water).Anyone know of an explanation or theory as to why it expands when frozen? Jim

Actually Jim, other substances do indeed expand when frozen, gallium, bismuth, acetic acid, antimony and silicon come to mind. This process has to do with the atoms in the crystal lattice in some substances being packed further apart than the liquid.

[Dutchdivco]

Ahh, but do they also expand when heated. Not argueing here, far from it.Just going by a stray comment on another forum, that SAID that H2o is the only substance that expands when heated or cooled.Wondered why. Another stray thought; Read up on the origin of DMSO, the source for MSM.Said it comes from algae, that grows in coastline wetlands. When the water evaporates, it carries the DMSO with it, into clouds, and down with rain. Absorbed into the soil, then into plants, eaten by animals, both of which we eat. This is why its so ubiquitous.My point is those who talk about using rainwater, and then distilling it, to get a 'pure' water to experiment with.DMSO would be in the rainwater, even after distilling, although admittedly in small quantities.And DMSO has some REALLY strange qualities! Wonder if some of the anamolies of water are because of the DMSO in it? I don't know if its even possible/practical to remove the DMSO.Anyway, just thinking,...Jim

[Moontanman]

Originally Posted by Dutchdivco

Ahh, but do they also expand when heated. Not argueing here, far from it.Just going by a stray comment on another forum, that SAID that H2o is the only substance that expands when heated or cooled.Wondered why. Another stray thought; Read up on the origin of DMSO, the source for MSM.Said it comes from algae, that grows in coastline wetlands. When the water evaporates, it carries the DMSO with it, into clouds, and down with rain. Absorbed into the soil, then into plants, eaten by animals, both of which we eat. This is why its so ubiquitous.My point is those who talk about using rainwater, and then distilling it, to get a 'pure' water to experiment with.DMSO would be in the rainwater, even after distilling, although admittedly in small quantities.And DMSO has some REALLY strange qualities! Wonder if some of the anamolies of water are because of the DMSO in it? I don't know if its even possible/practical to remove the DMSO.Anyway, just thinking,...Jim

Yes they expand when heated, water contracts until it at a certain point (cold) and then begins to expand as it freezes so do these other substances. Once above this densest point water and these substances expand as well (hot) What is DMSO?

Moderation Note: Responses dealing with DMSO have been moved to Dimethyl Sulfoxide

[Kharakov]

Originally Posted by HydrogenBond

In chemistry water is normally represented as a bent molecule with an almost tetrahedral shape with two hydrogen atoms and two non bonded electron pairs.
....
What they have found is the two non bonded electrons pairs sort of merge between where they thought the two non bonded electrons were, much closer to the oxygen atom.
....
When water forms ice then the tetrahedral sort of returns. But when water is hydrogen bonded to some proteins, the water is triangular. The bent shape allows the hydrogen to share the electrons on another water.

Side note for you (Bond, H-bond): 2 different groups (one definitely published in the Journal of Magnetic Resonance, the other I am not sure of at this point) are working on room temperature solid state water in various materials (it started with concrete).

One has approached this from the experimental angle, observing tetrahedral jumps with NMR, another has approached it from the theoretical angle calculating that tetrahedral jumps occur using mathematical physics simulations. Not all that sure who/what the other group is, I just know that someone approached it from the theoretical angle (I might be able to dig around and find who it is...).

k

[Essay]

Originally Posted by Kharakov

Journal of Magnetic Resonance,
k

Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C2 symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C2 jump rate is much faster than the tetrahedral jump rate. 2H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above.
For hydrated Zeolite A, the kinetic activation parameters (dH, dS) for the tetrahedral and C2 symmetry jumps are: dHtet = +17 kJ/mol, dStet = −109 J/(mol K), and dHc2= +19 kJ/mol, dSc2= −20 J/(mol K). For kanemite, dHtet = +23 kJ/mol, dStet = −69 J/(mol K), and dHc2= +23 kJ/mol, dSc2= −11 J/(mol K).

...C2 jumps???

Originally Posted by google:

"C2 jumps" NMR

A multinuclear nuclear magnetic resonance study of t-butylthiol
SANDRMAO OIBROEKAN' D RODERICKE. WASYL~SHEN
Depczrtnlerlt of Chernistry, Dc~lhortsie University, Hnlgczx, N.S., Ccznnda B3H 453
Received February 12, 1985
A multinuclear nuclear magnetic resonance study of t-butylthiol
or
http://article.pubs.nrc-cnrc.gc.ca/p...startPage=2926

In the rapid motion limit, the effect of jumps between sites of three-fold or greater symmetry is exactly the same as for rotational diffusion. Once this limit is reached, one cannot distinguish, for example, between 120" jumps or continuous rotation about a C3 axis. On the other hand, rapid jumps and diffusion about a C2 axis yield substantially different spectra (7-9, 11, 12). Theory predicts that 180" flips about a C2 axis in t-butyl compounds will result in an effective asymmetry parameter of 1....
The situation for more complex motion - e.g. a combination of C2 jumps and Cx jumps about different axes - is much more complex, and will not be dealt with here.
...
Since neither rapid diffusion or fast C3 jumps predict [asymmetry], the highly asymmetric lineshapes observed in this phase imply that C2 jumps must be involved in the reorientation of the molecule.
Further discontinuous changes in the deuterium nmr line-shapes do not take place until 164 K (d.o. compound) or 166 K (SD isotopomer), corresponding to the solid 111 --> solid 11 phase transition. At 164 K, the ...spectrum... undergoes further narrowing to a featureless peak of - 1 kHz in width with low intensity shoulders.

===

Ack! What an interesting way to waste a couple of hours.

So the C2 orientation is the one between the tetrahedral (C3) orientation (through the center of the face rather than thru the corners of the cube).
The one which HBond notes predominates in some bonding situations.
Thanks HB, ...interesting as always....
===

Kharakov, that was a fascinating link on the Zeolite/kanemite hydration studies.
Thanks mucho:

It's neat that they include the Entropy, dS (delta S), in their measurements of the kinetic activation energies for these different conformations of "orbitals." ...the tetrahedral is more stable by a few Joules (compare with the kiloJoules for the OH bonds).
===

Whatever the precise details are, IMHO it's obvious that the changing shape of water molecules in various conditions (including phase changes) affects its packing behaviour--and thus its volume.

...as to the hot water freezing faster "topic" I don't know, but the dissolved gases theory sounds plausible....
This would be a good Science Fair Project for some kids!


~

[logy]

Originally Posted by Dutchdivco

My 1st post, after intro'ing myself. Water is a fascinating stuff, no doubt.Read its the only substance that expands, when heated or cooled. (Not counting things like milk, which is largely water).Anyone know of an explanation or theory as to why it expands when frozen? Jim

umm the explanation is fairly streight forward:
generally liquids expand when heated and shrink when cooled because when they are hotter, the mulecules move faster and need 'room to move'.

water has an intersting charcteristic due to it's molecular V shape and strong H bonds, so that when it is frozen is takes more space for each molecule. i found a web page with a nice diargam that demonstrates that


at the top you have ice and at the bottom you have water. in water the V shaped molecules are closer to each other because the hydrogen atoms (small balls) are not bonded to oxygen (large balls) from another molecule, while in ice every hydrogen is bonded to an oxygen from another molecule (represented by the rods that are connecting the balls), creating that larger tertahedral shape.