Originally posted by jlafleur02
I have a question about freezing water. In a water line, when the water freezes The pipe will burst. There isn't energy being put into the water it
is actually being taken out of the "system". It produces a great force to burst the pipe. To me this defies the Laws of conservation of energy.
The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant
over time (is said to be conserved over time). A consequence of this law is that energy can neither be created nor destroyed: it can only be
transformed from one state to another. The only thing that can happen to energy in a closed system is that it can change form: for instance chemical
energy can become kinetic energy.
This is from wikipedia
When a force is create it is a form of energy. If I took a box that can expand, filled it with water, then hooked up an assembly of some kind to use
this force to create energy the water should experience a loss of mass or should show some temperature change.
I have several questions:
1. Does it take energy to remove heat from water? I know there are freezers and such, but I mean in nature does it take energy to freeze a pond?
2. how much force is need to burst these pipes and can It be accounted for as to where the energy to do this comes from.
3. I know that water expands due to its molecular structure when it freezes. How can it expand when its physical state is being lowered. As ice it is
a certain volume then it goes to water, the volume shrinks then to a gas the volume expands? also is there another compound that does this.
order to apply that quote from Wikipedia, you have to define what is included in the "closed system". A water pipe isn't really a closed system,
it's exchanging heat with the surrounding environment. So we can't apply a law relating to a closed system to something that's not a closed
But let me see if I can answer your questions without having to get into that.
The answer to question 1 is best (to me) described by this diagram:
Note I will refer to temperatures in degrees C.
Take a 1000 gram block of ice at a temperature of -40 degrees C, apply heat to it, and it warms up, to -30, to -20, to -10, and then 0C. By the time
the ice initially gets to 0 degrees C, we have added 20,000 calories of heat energy (40 degrees x 0.5 specific heat in cal/g-deg C x 1000 g), and then
an interesting thing happens. Even though we are still applying heat to it, it doesn't continue to get warmer like we might expect. The temperature
gets "stuck" at 0C which is what the horizontal line near the left of that diagram labeled "melting ice" represents. This interesting phenomena is
called "heat of fusion" not to be misconstrued with any type of nuclear fusion. It takes a relatively large amount of energy to turn the ice into
water, about 80 calories per gram. This means we have to add 80 cal/g x 1000 g = 80,000 calories of heat energy. the amount of energy required to go
from 0 degree ice to 0 degree water.
This "heat of fusion" I think is the key to answering your question. The 80,000 calories of heat energy doesn't increase the water temperature at
all, it's energy that's being stored in the water to make it a liquid phase instead of a solid phase, by breaking the chemical bonds of the ice.
Once the 80,000 calories is added and all the ice is melted, if you apply another 100,000 calories of heat, the water will increase in temperature
from 0 degrees to 100 degrees C. Then the temperature gets "stuck" again for the next phase change to steam, where we must apply 539,000 calories of
heat to go from 100 degree water to 100 degree steam.
So that's the answer to your question 1 in reverse, it shows how much energy must be added to the water to heat it from ice to a liquid to a gas (at
normal atmospheric pressure, at sea level). That's going from left to right in the diagram. So to answer question 1, just do the reverse, take
exactly that number of calories out of the water and you lower the energy and change the phases in the reverse direction (go from right to left in the
diagram). Does this make sense? Are you with me so far?
Your second question "how much force is need to burst these pipes and can It be accounted for as to where the energy to do this comes from" was
partly answered here:
Originally posted by 4nsicphd
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.
That tells you how much pressure is needed to burst the pipes, 800 PSI rating for copper and it would need to have a
rating of perhaps 300,000 psi to not burst. Where does the energy come from?
Remember above when we added 80,000 calories to the 0 degree ice to convert it to 0 degree water? That's where the energy comes from, and the force
is generated by converting that latent heat of fusion energy into molecular bond energy exactly as described in this post (which also answers question
Originally posted by 4nsicphd
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
That's essentially the answer, although there are 16 different types of ice and I thought the Wiki was correct that the hexagonal crystalline form is
the most common type:
Ice may be any one of the 15 known crystalline phases of water.
-ice Ih: Normal hexagonal crystalline ice. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic.
-ice lc: A metastable cubic crystalline variant of ice. The oxygen atoms are arranged in a diamond structure. It is produced at temperatures between
130 and 220 K, and can exist up to 240 K, when it transforms into ice Ih. It may occasionally be present in the upper atmosphere....
-ice III: A tetragonal crystalline ice, formed by cooling water down to 250 K at 300 MPa. Least dense of the high-pressure phases. Denser than
So 4nsicphd is right about the fact there's a tetragonal type of ice, but it's a high pressure phase of ice and it won't burst your
pipes because it's less dense than water.
When you apply that 80,000 calories to the water it's sort of like pumping water up to a water tower, it becomes stored energy. When you allow the
water from the water tower to fall back to ground level, it can do work like power a water wheel, or hydroelectric dam. When you allow 4 degrees
liquid water to turn to -1 degrees ice, likewise it's capable of doing work by releasing the 80,000 calories of stored energy which was previously
added in the heat of fusion phase change from ice to water. The work is actually done by the millions of molecular bonds forming as the water freezes
as 4nsicphd describes.
Regarding question 3, you almost answer your own question: "I know that water expands due to its molecular structure when it freezes. How can it
expand when its physical state is being lowered. As ice it is a certain volume then it goes to water, the volume shrinks then to a gas the volume
expands? also is there another compound that does this."
Liquids and gases don't have crystals, so the molecular spacing is determined by phase, temperature, pressure etc. When materials turn from liquid
into solid materials, some materials like water, form crystals. The ice crystals happens to take up more space than the liquid form, because of the
crystalline structure of water ice crystals which 4nsicphd described pretty well, it has to do with the shape of the water crystals and the spacing
that results between the molecules in the crystal lattice.
Other compounds that expand on freezing are: silicon, gallium,
germanium, antimony, bismuth, plutonium and other compounds that form spacious crystal lattices with tetrahedral coordination