why water has maximum volume at 4 deg. c at 1 atm

I thought you'd never ask.

Essentially, water molecules hide behind other molecules when it's cold, but then come out as they warm. But enough of this technical talk - here's a link to the process in layman's terms.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFN-3YMFMRX-X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=10&md5=742f3cdaf0cf27ff16a08d5f278dd397

HE is a genius. Water is the only material with this characteristic. Were it not so, cold area lakes would freeze solid from the bottom and never thaw. WE would not exits.

There are several liquids with this property. He⁴ is the only other common one.

Bismuth

What a marvellous thing this................ evolution................ is!!!!!!!!

I plead guilty to being a smart-alec but not to being a smarty-pants.

I did see the OP had the maximum/minimum reversed, but assumed he simply said it backwards.

There are lots of engineers and scientists on this forum and many of us do see He often. It's not a rare liquid to me.

I think the angle explanation is not generally considered sufficient nowadays. There are a number of papers on possible causes for the anomaly; I cited one. Fell free to cite others, but don't flame me for reading journal abstracts.

Cheers.

Helium becomes a liquid near absolute zero, somewhere in the neighborhood of -270 degrees Celsius. This does not occur naturally on the planet, thus water is the only common substance which exhibits this property. This is an example of exactly my original point - if you look for extreme conditions you will find uncommon behavior. Extreme conditions and consequent uncommon behavior are not the basis for understanding the nature of our world.

The effect that temperature and liquid vs. solid-state has on the angle between the two hydrogen atoms and the oxygen atom is not an insufficient explanation. It is a simple fact that was observed long ago. What may be considered insufficient is that it is stated as an empirical fact, without further explanation. As to why the angle changes, that is clearly a question of the mechanics (perhaps quantum) within the molecule itself, and I don't know anything about that.

But unless the original post regarding water density was asking for a quantum mechanical description of the H2O molecule, the explanation of the angle change is both necessary and sufficient to answer the question.

Sorry for the smarty-pants remark. It was not personaly directed, but a general observation about people who make things more complex than they need be. An example of this is that we can use the physics of waves to predict the movement of a wave in water, without knowing anything at all about the makeup of water on a molecular or atomic basis. One can always ask why the water moves as a wave, but that doesn't invalidate the physics and mathematics that predict the wave movement. Einstein said everything should be made as simple as possible but no simpler. Newtonian physics was enough to get us to the moon and back, even though General Relativity had been around for almost half a century. We model things to the point where we can explain them. We increase the complexity of the model only when the original model fails to answer questions of interest. This is the history of science.

For me , it is important to be as accurate as I can without getting pedantic. I don't deliberately "dumb down" science unless I'm talking to a child. The OP seemed to be asking a question appropriate to a University student and I answered accordingly (plus the wisecrack, which I probably should have omitted, but...).

When I say the angle explanation is insufficient, that is because it is so. You cannot cause the density to vary by simply changing the angle. A better explanation of what happens is that there is a "competition" between covalent bonds (which have a unique angle in water) and hydrogen bonds (which have a different unique angle in water). At just below 4 °C there is, in effect, a potential well where the two regimes are mixed just so as to give the maximum packing. The angle is the tail of the dog; it does not wag the dog.

Now, there are competing theories about what the structure looks like at maximum density (i.e. how bonds are broken or how molecules are packed "into" one another) and it takes someone with far more chemistry knowledge than me to sort that out. There are even those in QM who think all this to be connected to zero-point energy. So, I referred the OP to a fairly decent paper; if he wants more, he can follow that. And, by the way, I do not intend the bond explanation to be seen as a final definitive answer, but rather one that is probably fitting for a university student in a beginning course.

And, I disagree with you about helium and this is why I think it important: Many people cite the "special density property" of water as being necessary for life and therefore proof of intelligent design. The fact that any other fluid (yes, in my world, helium is common but the point is valid even if you define it as uncommon) has this property deflates the ID claim. In fact, it is not clear that this property is needed for life. To wit, many small lakes freeze solid and then thaw. Other liquids without this property melt OK. That may be an open question, who knows?

Not getting into intelligent design vs. evolution. Not going there. Comment about the density of water as a function of temperature and state was simply an observation that aquatic life as we know it could not survive a planet in which the water it depended on for life froze solid every winter. If you don't believe aquatic life (fish/amphibians) antedated reptlles, mammals and birds then the point is moot regardless.

Extreme conditions not found on planet earth, are not required to disprove the idea that water is the only substance that exhibits a charactersitic of expansion upon solidification or alternately a liquid density greater than solid density.

Bismuth, gallium, silicon and germanium all exhibit this property at atmospheric pressure and a range of temperatures begining around room temperature for galium and slightly more for bismuth...but nothing extreme or exotic is required.

The exceptions to the claim are plentiful and do not require extereme conditions. It is time to retract the claim about water being the only substance to exhibit this property.

You wrote..."It is not the volume that is maximized at 4 degrees Celsius, it is the density. "

Hmmm... How do you maximize density without maximizing volume and without changing the mass? and if your statement is correct, why will a glass bottle explode when water freezes inside...

Wangito.

Question....................you almost fill a bottle of water and bring its temperature down to 4⁰C .................you will find that the volume decreases to minimum volume..............then as you drop the temperature to freezing.................volume increases as the water freezes............ and smashes the bottle??????

Density equals mass divided by volume. For a given mass, density is maximized by minimizing volume. When you approach freezing (0 degrees Celsius), the angle between the two hydrogen molecules with the oxygen molecule at the vertex increases slightly, and that expands the volume of the molecule, while its mass stays constant. Hence density decreases slightly, and ice floats (just barely). So the whole picture is, starting with summer temperatures, as the earth cools in fall and winter, the water at the top of a lake or even the ocean cools the fastest, and when it gets to 4 degrees C where it is densest, you get "turnover" where the water that was at the top changes places with the warmer less dense water that was below, and when the new top water gets down to 4 degrees Celsius it basically stays put and gets even colder, and starts to freeze from the top on down, preserving the warmer denser water at the bottom. Hence, as the other contributor stated, life exists on planet earth.

..................or............convection currents cease because the water at the lower level (not necessarily the bottom-because water is a poor conductor of heat)) is at max. density.

If you take a specific amount of water and measure its volume at for example at 20°C and measure its volume again at 4°C, you will find that it has "SHRUNK" slightly.....it is now at its maximum density though, minimum volume.

You seem to misunderstand what is happening at 4°C......I hope this helps you to correctly understand better.....

As another responder noted, it is this property of colder water being denser but frozen water being lighter that is responsible for life existing on the planet.

I think that should read "....life as we know it existing on the planet".

You have been given several good answers already, but do remember that this is what allows fish to remain unfrozen in deep water lakes as the water in winter gets colder or freezes, it rarely freezes more than 1 meter or so, ice fishing also could not take place either if it was not for this interesting effect!!!

What about 'fish anti-freeze' ? This doesn't negate your point Andy, but it's interesting all the same ; http://www.msnbc.msn.com/id/13426864/

For water under 1 meter deep, where it can freeze all the way to the bottom.....

That's another interesting web page Kris................you are doing well.

One thing I would like to know from Christina Chang is how this fish developed, over a period of time, or driven by a need to evolve AFGP, to stop its blood freezing.

Interesting...............how did the fish know it needed anti-freeze............and how did it know what to develop.

Boy I wish I had had some of that anti-freeze in me sometimes.

I used to drink several different kings of anti-freeze sometimes..................vodka, brandy, scotch...............and of course rum.

Yes water is an extraordinary substance. It's density has already been mentioned.............but, water is anomalous in nearly all of its physical and chemical properties.

The shape of the water molecule itself is interesting, not to mention the combination of two gases forming the most plentiful substance on earth.

This molecule acts like a tiny magnet, with its negative pole up by the Oxygen atom and the positive poles down around the Hydrogen atoms..............this gives water its relatively high surface tension. This is also why water beads on a smooth surface.

Water also has the ability to absorb large quantities of heat:-

0⁰C - 100⁰C.....................4,19kJ/kg⁰C

Latent Heat of Vapourization (Entropy)...............2 270kJkg^-1

This makes water an excellent medium for fire fighting.................and during the day absorbs much of the heat from the sun and gradually releases it during the night keeping our temperatures here on earth at a livable level................not to mention the role it plays in the earths major wind systems and local wind.............sea and land breezes.

Another amazing thing with water is is rain or more correctly.............precipitation.

The atmosphere is full of extremely fine particles of dust, smoke, soot, sea salt and of course water vapour..............as the air cools water vapour condenses on these tiny nuclei, forming minute droplets of water which become visible in the form of clouds. a small fluffy cloud (Cirrus) can contain anywhere from 100-1 000 tonnes of moisture, in the form of ice crystals.............it can take a million or more cloud drops to make one raindrop.

Just thought that I would mention a few points on our most valuable resource.

Water has a unique 'anomalous' expansion prpoerty .

The expansion of water is unique to other materials.

Another substance sharing similar properties is Ammonia. Although it is uncommon (actually impossible) to find Ammonia frozen in nature on Earth.

Just my two cents. Dragon

Dear Mr. irshy84,

The water when cooled the volume will shrink, according to the CO-EFFICIENT OF APPARENT EXPANSION.

BELOW Zero Deg. C, the water becomes SOLID as Ice and the co-efficient of Linear Expansion of ice varies. from that of water. POSSIBLY the phase change of liquid to solid causes the effect.

The Water will have max Weight, for a given Volume of water,at 4 Deg.C (OR) MINIMUM VOLUME, for a given weight of water, at 4 Deg.C. pressure being 1 atm in both cases.

Your statement " water has a maximum volume at 4 degree c and 1 atm " is error.

Pl. clarify.

RAJESWARI.

Yep. Try "Thermodynamin Properties of Fluids", any edition. Mayhew and Rogers are the authors.

The feature is pretty handy. The outcome is the survival of marine animals in the liquid phase beneath a solid phase at the top surface, as might be found in, oh, frozen lakes, for example.

It's a wonderful substance, water. Hydrogen Sulphide, its equivalent in the next row down in the Periodic Table (as Oxygen is to Sulphur), is a gas at ambient temperatures and pressures. If there were no hydrogen-bonding between water molecules, water might not be a liquid at all, and life as it is currently understood might never have got started.

If you take a volume of water at 4 degrees and heat it, the volume will increase. And if you cool the 4 degree water, the volume will increase also. So it seems the 4 degree water is when the water has the minimum volume. The reason this happens is from the motion internal to the H2O molecule. Temperature changes these motions. And those motions change the volume of space, the actual size, of the molecule.

Particles, atoms, molecules and everything else, changes physical size, with temperature. And some can change in different ways. When you heat a particle......it shrinks.......but at the same time, the bonding distance can expand. So it's the ratio of particle size change with distance change that can determine the final result. Some structures will shrink and others expand.....with temp.

We see the obvious changes in size, with form .....and we call it a phase change. But in the future we will understand all these unknown, un-detected "phases" of matter. And it's all the result of the "quantum" effect. A mysterious probability dynamic. But very few realize that particle size changes with energy. Or acceleration. Or gravity.