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General Science => General Science => Topic started by: thedoc on 13/03/2015 10:13:19

Title: Why does water expand when it freezes?
Post by: thedoc on 13/03/2015 10:13:19

Why does water expand when it freezes?
Asked by Martin


                                        Visit the webpage for the podcast in which this question is answered. (http://www.thenakedscientists.com/HTML/podcasts/naked-scientists/show/2009.10.11/)

[chapter podcast=2074 track=09.10.11/Naked_Scientists_Show_09.10.11_4754.mp3](https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2FHTML%2Ftypo3conf%2Fext%2Fnaksci_podcast%2Fgnome-settings-sound.gif&hash=f2b0d108dc173aeaa367f8db2e2171bd)  ...or Listen to the Answer[/chapter] or [download as MP3] (http://nakeddiscovery.com/downloads/split_individual/09.10.11/Naked_Scientists_Show_09.10.11_4754.mp3)

Title: Why does water expand when it freezes?
Post by: Nizzle on 17/08/2009 14:02:52

I can't answer all your questions, but i can answer some.

Why does water expand when it's freezing: because it's maximum density is at 4°Celcius.
This is also the reason why water is fluid under great pressure. You won't find any frozen water pockets on the bottom of the ocean neither, because the pressure will make the water be at it's maximum density.

Maybe someone else can explain why the density of Ice is lower than 4°C water...

Title: Why does water expand when it freezes?
Post by: DrChemistry on 17/08/2009 14:59:27

I'll give it a shot, see if I'm correct [:)]

As you know, water is a really characteristic compound in comparison to other compounds. Many compounds contract when they are frozen, just like your thermometer drops when it gets colder. Water differs because, as Nizzle correctly stated, it's maximum density occurs at 4 degrees celcius. This means that below 4 degrees celcius it can do nothing but decrease its density and expand, as it could not have a greater density (The exact reason why ice floats).

Another thing which plays a role is its polar nature. What basically goes on here is related to its structure and polarity. Water has an sp3 hybredization, but due to what we call "Valance Shell Electron Pair Repulsion" (or short VSPER Theory), the angle between the centered Oxygen atom and two hydrogen atoms is about 105 degrees. I will return to the structure in a moment. Water is also polar. Oxygen is more electronegative than Hydrogen and greedily pulls Hydrogen electron towards itself. This makes Oxygen slightly negative, and hydrogen slightly positive. This enables water to form what we call 'Hydrogen Bonds' (Process: Hydrogen Bonding). In water these bonds will form, break and form again on a new. Freezing causes less molecular activity because it means it's a drop in energy. Hydrogen bonds become more stable, and order themselves as a quite spacy hexagonal structure, due to its structure (It expands, taking up more space).

I am not sure what force it exerts when expanding though  [:)]

P.s. I should add that this is for 1 atm (Atmospheric Pressure), which is the equivalent of 101325 Pa. Also as Nizzle stated, greater pressure ensures water as liquid.

Title: Why does water expand when it freezes?
Post by: thedoc on 13/03/2015 10:13:19

Listen to the answer to this question on our podcast. (http://www.thenakedscientists.com/HTML/podcasts/show/2009.10.11/)

Title: None
Post by: Richard on 10/02/2010 01:09:52

The answer was helpful, though I have a follow up question. If the water is in a confined space, say a bottle, before freezing, then once all the water has frozen the air pressure inside the bottle rises. This must meen that the air inside the bottle is not filling in that 'space' inside the ice crystals. Does this meen that inside these cystals is a vacuum or is it just that air is inside these crystals but at a lower pressure to the surrounding atmosphere? If not, what exactly fills these crystals?

Title: None
Post by: Haider Riaz on 03/02/2014 13:32:36

Can anybody please answer this question not according to Chemistry?

Title: None
Post by: Rob on 19/03/2014 23:18:24

If by non-chemical you mean simpler, maybe I can help. In general, liquids, and other states for that matter, expand as they get hotter and contract as they get cooler. That happens with water, too, but once it gets to freezing temperature, the molecules basically lock in place in a crystalline structure that actually has more space in it than there would be if the molecules we're still floating freely in liquid form.
I'm not sure if I added anything useful to the above explanations, but it's simpler at least.

Title: None
Post by: Guest on 31/10/2014 15:39:10

But how do the hydrogen bonds cause the water molecules to move further apart? Shouldn't the attractive forces of the hydrogen bonds cause the water molecules to move closer together?

Title: None
Post by: Anonymous on 05/11/2015 01:57:48

This was an excellent website because I had to do a project on this... but doesn'the some of the air around the ice freeze as well, therefore making the ice bigger? Also, does the mass of the water matter if it grows or not, when it freezes?

Title: None
Post by: Lunanox on 22/12/2015 08:28:52

I am strongly certain that air does not contribute to the increase in size of ice. All it just is it makes the air cold. As for the mass, I'm not sure about that but I am confident it does affect.

Title: None
Post by: sdfasdf on 21/09/2016 03:04:46

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