WATER ? please help explain this

What I find fascinating about water is that it's made up of two gases (Hydrogen and Oxygen) that when you apply a flame to they burn like no other but when you bring them together (water) they extinguish flames.

Perhaps it's the Hydrogen that causes expansion when starting to freeze. Maybe we just need to break the water down to understand whats going on.

a simple experiment can be done to show how water can burst pipes. Fill a glass bottle with water and put on the cap. Put the bottle in a freezer and check on it 24 hrs later. come back here and report what you find.

As someone else said, the energy is already in the Water, because before it freezes it has more thermal energy. When it freezes it loses this energy. At first, as it cools to zero degrees C, the energy lost just goes to the outside environment, more or less uselessly for any system. Once it reaches freezing point it has to freeze, which is where the enthalpy of fusion comes in.

This is the energy used to break your (hypothetical, I assume) bottle of water, AFAIK. This energy is 333.55kJ per kg of water. Assuming my calculations are correct, thats roughly the same energy required to make a 747 move at a (slow) walking pace.

So, somewhere in that should be the energy required to break pipes, bottles of water, rock, roads, etc.

Slightly off topic, but this is a facinating documentary about water

topdocumentaryfilms.com...

A molecule of water is composed of 2 Hydrogen atoms and 1 Oxygen atom, this is why you see it referred to as H2O. Various atoms have positive and negative charges which attract and repel each other. The hydrogen and oxygen atoms attract each other such that they form bonds with other water molecules. Look at the picture on this page to help you visualize: users.rcn.com...

In liquid water, the molecules move freely around, picture them tumbling around each other, forming, breaking, and reforming bonds with other molecules. Now when the water cools, as heat is removed, the molecules lose energy and stop moving around so much, which causes the attractions/bonds to align them into a lattice structure, which rigidly spaces them evenly and farther apart than when they were more energetic and chaotic, thus it takes up more space. As for where this "force" comes from, it is the force of attraction and repulsion between the hydrogen and oxygen atoms, the molecules to the other molecules, the sharing of the hydrogen atoms with the oxygen atoms of other molecules, aka "hydrogen bonds".

It takes heat to break these bonds, which is why ice is more strongly bonded. As you heat up the ice the energy is able to overcome and break some of the bonds, which allows the molecules to move around more and you get liquid water. Add even more heat and you can break the rest of the bonds and there is nothing left to hold it together and it becomes vapor.

So the answer to your question of where is the energy coming from to give ice the power to break a pipe, is that due to the LOSS of energy (heat) the water molecules slow down enough that the attraction of its hydrogen bonds forces its molecules to settle into a stable structure which is less dense and thus expands.

It can seem counter-intuitive that the tiny force between atoms can "break a pipe", but just remember that the walls of a PVC pipe are just atoms too, and the atoms of plastic and metal that make up the walls of a pipe are bonded together by similar bonds, but just in a relatively thin layer as compared to the expanding interlocked lattice of hydrogen bonds of the ice. The number of interlocked hydrogen bonds just ends up having more strength than the wimpy plastic atoms trying desperately to hang on to each other

P.S. I wrote this at 7:30am, and have been up all night with a cold and drinking Nyquil, so everything I said is probably not quite accurate, but I was trying to phrase it in a way that was easy to envision and understand. I just realized that I typed way more than the couple of sentences I meant to. In fact I am now noticing that just the P.S. is turning into a novel. I think I should just shut up and go to sleep now.

Why does a rock fall to the earth when you release it from your hand? It takes energy to hold the rock? Answer: the force of gravity. Gravity is of course a total mystery but the idea is that the rock is subjected to a force that was previously counteracted by the force of your muscles. This is similar to the water question.

When the water freezes the molecules re-arrange...not sure of the details but it's intermolecular forces that come into play in this example.

To put it in another way, the energy comes from the bonds between molecules....you'll have to google the details.

Blazers' answer above is much better than mine.

Originally posted by Seed76
reply to post by davespanners

 

Yes indeed. It´s fascinating the amount of force that is produced by the expansion of water has when it freezes.

Peace

And that is a direct result of water's bulk modulus properties. Water is almost incompressible. Almost, but not quite. That is why a belly-flop into the pool hurts. At 0 C, the compressibility of water is 5.1×10−10
Pa^−1.
A number of prior posters have touched upon the answers to the OP's questions, without really hitting them dead center. The answers lie in the laws of thermodynamics, and perticularly the second law. "It is impossible for a process to have as its sole result the transfer of heat from a cooler body to a hotter one." A second key is the polar nature of a water molecule. A water molecule is a dipole. That means that while each of the atoms in the molecule is neutral, having an equal number of electron and neutrons, the arrangement of the atoms gives on part of the molecule a charge component.The molecule forms a V, with the O atom at the vertex and the H atoms at the tips of the arms. The arms are at an angle of about 105 degrees. Since the O is more electronegative, that part of the molecule is slightly negative and the arms of the V are slightly positive. Each molecule can form a hydrogen bond with 4 other molecules in a tetrahedral form. Now these attractive forces are not really strong, but there are really a lot of them - roughly 15,000,000,000,000,000,000,000,000 molecules in each pint. Think about what that many forces, even though small, can do.

reply to post by jlafleur02


Ok that is new to me, I was unaware that theory had been replaced, so thanks for the update. I think the point that the energy required to burst the pipes comes from the thermal energy contained in the water still holds. As the pressure goes up, the temperature goes down, so you have perfect conservation of energy.

The specific heat capacity of water is 4200 J/KG/C. That is, it takes 4200 Joules to raise the temperature of 1Kg of water by 1 degree Celsius.

Conversely, the water must lose 4200 Joules of energy to cause a drop in temperature of 1 degree in 1Kg of water.

www.physlink.com...

Whether freezing or heating water, there is a transfer of energy. As described above, when water is heated, energy is transferred from the warmer surroundings to the colder water. Conversely, when the water is cooled, the heat of the warmer water is transferred to the colder surroundings.

When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%

This unusual behavior has its origin in the structure of the water molecule. There is a strong tendency to form a network of hydrogen bonds, where each hydrogen atom is in a line between two oxygen atoms. This hydrogen bonding tendency gets stronger as the temperature gets lower (because there is less thermal energy to shake the hydrogen bonds out of position).

www.iapws.org...

So, you have a pipe with water closed off in it. As the temperature cools, the water initially contracts, thus allowing more water to be forced into the closed off pipe. Then, as the water begins to form hydrogen bonds as it freezes, the crystalline structure changes and causes an expansion. Then....BURST!

So, in conclusion, yes it does take energy to freeze water and burst a pipe.

Originally posted by -PLB-
reply to post by jlafleur02

 

Ok that is new to me, I was unaware that theory had been replaced, so thanks for the update. I think the point that the energy required to burst the pipes comes from the thermal energy contained in the water still holds. As the pressure goes up, the temperature goes down, so you have perfect conservation of energy.

edit on 31-12-2010 by -PLB- because: (no reason given)

Its not thermal energy. Freeze a drop of water. there isn't any pipe or tube to put pressure on. The drop still expands. The energy of pressure that is present during the expansion in a tube which cause the pipe to burst is still there but the frozen water drop has nothing to exert that pressure on. so if it is thermal energy then with the absence of the force of pressure being shown we should see thermal energy or heat being released that would equal the energy of pressure if the water was in a contained system. I would say this is a mechanical energy that is cause by the interaction of the molecules.

I would also say that ice is the natural state of water and adding energy to it disrupts this state.

Originally posted by jlafleur02
so if it is thermal energy then with the absence of the force of pressure being shown we should see thermal energy or heat being released that would equal the energy of pressure if the water was in a contained system. I would say this is a mechanical energy that is cause by the interaction of the molecules.

I would also say that ice is the natural state of water and adding energy to it disrupts this state.

I think it is the other way around. If the H2O can expand freely, there is no additional heat being released. The H2O just follows the temperature of its surrounding. When the H2O can not expand freely, thermal energy is being transfered to pressure, so the H2O cools down more than the environment. But if thats true, the energy could also come from the environment. I have to agree that this issue is a bit counter intuitive .

I think we need to calculate the amount of force that water will exert, the amount of heat lost during the freezing phase, and the amount of heat that is needed to thaw the ice.

convert all measurements to a common unit do some math then go from there. I am no mathematican, can't even spell it right.

Any numbers guys out there?

Originally posted by jlafleur02
I think we need to calculate the amount of force that water will exert, the amount of heat lost during the freezing phase, and the amount of heat that is needed to thaw the ice.

convert all measurements to a common unit do some math then go from there. I am no mathematican, can't even spell it right.

Any numbers guys out there?

My scientific calculator is at the lab, but here is some information from which calculations can be made.
When water freezes, it gives up what is called the "latent heat of fusion" which is 334kJ/kg. So you can't do your calculation anyway without knowing how much water is to be frozen in the pipe. 1 gallon of water weighs (at sea level on earth) about 4 kg. There are about 12 gallons of water in a 10 foot long 3/4 inch water pipe so about 4000 kilojoules of heat is given up to the surroundings when that water freezes. The heat isn't "lost." It is transferred to the pipe and whatever is around the pipe.
When water freezes, it expands about 9%. So you're trying to squeeze 109 whatevers of water into 100 whatevers. The bulk modulus of water is 2.2 GPa So, to compress the water that much requires a pressure of .09*2.2, or about 2 GPa, which translates to a little over 290,000 psi. That's why your pipes burst. A regular PVC water pipe (3/ inch) is supposed to be good to about 1500 psi. High pressure is rated to 2200 psi. Copper is only good to about 800 psi.
BTW, the same abount of heat transfer is needed to melt ice. And all of the above assumes standard atmospheric pressure.
So, either keep your pipes warm or replace them al with high pressure stainless (grade 300 or better.)

reply to post by 4nsicphd

Interesting stuff. Useful knowledge. Thanks for that. Just a correction though on one point.
Where you said:

Originally posted by 4nsicphd
There are about 12 gallons of water in a 10 foot long 3/4 inch water pipe so about 4000 kilojoules of heat is given up to the surroundings when that water freezes. The heat isn't "lost." It is transferred to the pipe and whatever is around the pipe.

something went wrong with your calculator I think, as it's nowhere near 12 gallons in that pipe.

If we have a length of pipe with an ID of 3/4" (so D=0.75" and R is 0.375") and a length of 10 feet (120 inches), then its volume can be calculated via the formula for the volume of a cylinder as:
pi * radius squared* height

So, we use pi * 0.375 squared * 120, which gives us
53.04 cubic inches (rounded off).

As one US liquid gallon is 231 cubic inches, then what we actually have in the pipe as liquid water would be 0.2297 gallons, which is near as dammit to 0.23 gallons. So, a tad under a couple of pints.

No offense. Just saying, not criticizing by any means.

Best regards,

Mike

reply to post by JustMike


You are right about the volume calculation. I used an online volume calculator and I know better. That only affects the latent heat of fusion calculation and not the pressures, though. It's still going to burst the pipe.

Originally posted by Optix
being captain obvious here.... pipes bursting in the winter is from the pressure of water behind the ice blockage that keeps building up (17-20psi) and the contraction of the steel in the pipe making it smaller.

Now freezing water in a sealed bottle doesn't the air have to move somewhere? also the contraction of the bottle itself.

Again, this idea is entirely wrong. Want proof? Do you keep your water taps on to prevent this buildup of pressure? No. So anytime your water tap is off, you are blocking the water. I can tell you, the breakage happens where the ice has formed and needs to expand. not in the liquid water.

reply to post by Aliensun


i worded that wrong i meant to say when the ice expands and the pipe contracts, plus the pressure does not help.

The water molecule is roughly shaped like the head and ears of Mickey Mouse, where the 'ears' are hydrogen atoms and the 'head' is an oxygen atom. Since hydrogen will eagerly share it's electron, it acts like a 'positive' pole of a magnet (each 'ear' acts as a +1), and the head, oxygen, is willing to take on 2 electrons,so the head is a -2. This means the top of the molecule is positive relative to the bottom, and will result in the entire molecule acting like a v-shaped magnet.

For the sake of simplicity, I'll use a 2 dimentional example.....

Cut out a bunch of identical Mickey Mouse heads and put as many as you can on your kitchen table without overlapping any of the Mickeys. This represents water at 4 degrees Celsius, the maximum density of water. As the water gets closer to zero, the Mickeys begin to align themselves so that they are all upright, side by side, in an orderly 'brickwork' that I will call 'ice'

V V V V V V V V V V
_V V V V V V V V V V = ICE
V V V V V V V V V V
_V V V V V V V V V V

As you line up all of the Mickeys, you'll find that they take up a lot more space on the table, and you will no longer be able to fit them all on the table. The left-over Mickeys represent the expansion of water as it crystallizes to ice.

I hope this helps you visualize what's going on. Water is one of the most incredible molecles!

as matter goes there are four states of matter we are concerned with
solid liquid gas and plasma
what we are talking about here is a transformation from one state to another

for fun watch this following clip
beer freezing instanly


now the tap or shock of the bottle on the bench sets of a cyrstaline reorginization of the liquid into on orginized state
the solid state
so is the sound shock aligning particals that normally self orginize?
the reason i included the video was to show the process of freezing sometimes has to do with outside influences

my personal thought on all of the ops questions
is we dont understand the electro potential energy requirements of the H H O as a soild water gas or plasma
i imagine ice as a crystal formed from an outside force acting to arrange electro cemical bonds
xploder

I asked your same original questions to my dad when I was about 10. The energy that is used to expand the water is not heat. It is in the movement of the electrons. when enough heat energy is removed the other energy becomes stronger and can now shape the molecules. The new shape is bigger than the liquid shape. The energy is always there but not able to act due to the heat keeping everything moving. Just to let you know that water does decrease in volume until it freezes and right at the point of solidification it expands. After that if it gets even colder the water will again reduce in volume. I was also told back then that this is a good thing because if it did not happen frozen water would sink so a lake would freeze bottom to top instead of the other way around. this would keep the bottom of lakes frozen all year round with just the top two or three feet thawing out. I was also told that water is the only thing known to expand at the point of solidification. Now that was 40 years ago so maybe they have found something else that does it.
P.S. Thanks for reminding me of a very good memory. We were camping when I had this discussion with him.