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downquark1
26-11-2003, 13:48
Anyone want to post an answer to an everyday question?

I'll go first:
Why does water expand when frozen when everything else contracts?


Also judging by the weight of the water compound it should actually by a gas at room temperature

This is because of an obscure little phemoninon in chemistry called a permanent dipole.

Bascially one part of the molecule is more negative than the other parts
http://www.chm.bris.ac.uk/~chjnh/gcse/pics/water_trimer.jpeg

This causes them to be attracted to each other at certain angles
https://www.cableforum.co.uk/images/local/2003/11/2.gif

When the temperature is below 0˚C they lock together in a strange hexagonal shape (this is called a hydrogen bond)
http://www.mrs.umn.edu/~goochv/CellBio/lectures/water/Image126.gif
This is apposed to other chemicals that 'freeze' solid in a nice stacks
http://forum.nthellworld.co.uk/attachment.php?attachmentid=368

This leaves the 'ice' with less density than water.

When the temperature rises above 4˚C they gain enough energy to break free of these locks and are able to flow around each other closely. But the attraction is keeping them close together - this is liquid water. When the temperture rises above 100˚C they have enough energy to break the attraction completely and become gas (steam).

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It can be anything at all - I for one don't understand the off-side rule :D

Dave Stones
26-11-2003, 13:59
thank you for re-opening the wounds of my a-level chemistry lessons :cry:

___

Paul
26-11-2003, 15:08
Next time that question comes up in my daily conversations I will be very grateful I now know the answer ....... :)

Xaccers
26-11-2003, 15:15
thank you for re-opening the wounds of my a-level chemistry lessons :cry:

___

Hey at least it's inorganic chemistry, nice and easy.
It's the organic stuff that threw me, but then I did have the greater daemon of chemistry standing in for that part of the course.
One minute something would be a nuclearphile, next it would be an electrophile, she didn't make sense.

Ramrod
26-11-2003, 15:28
Thanks for the nightmares downquark.....



Can we post anything of technical interest here?
...what the hell, here goes....

If any of you indulge in exercise (football, tennis, martial arts, running etc.), do not strech before exercising. Strech afterwards! Just warm up properly before exercise. You lose about 22% power by streching and you are at increased risk of injury as well.
(my 2cents)

downquark1
26-11-2003, 15:44
Well, I was bored, so I thought I would spread the boredom ;)

Here's another one:

If you eat cold food you can loose weight:

This is because you are burning callories heating the cold food in your body, so in theory if you make the food cold enough you can eat fatty food and not gain any weight!

I guess the water explaination was aimed at people who didn't take the sciences in further education. It's very confusing because at KS3 and GCSE you are taught that things contract when frozen, but then you wonder why milk breaks the seal in winter.

bopdude
26-11-2003, 16:46
Well, I was bored, so I thought I would spread the boredom ;)

but then you wonder why milk breaks the seal in winter.


You meean that it isn't the poor little robin's wanting a drink ????? :p :dunce: ...lol

downquark1
26-11-2003, 16:54
You meean that it isn't the poor little robin's wanting a drink ????? :p :dunce: ...lol
:erm: No I mean it expands out the top of the bottle

This thread isn't going as I planned :(

Theodoric
26-11-2003, 20:22
OK, while we're on the subject of ice, why can you easily skate on ice? The answer you're likely to get at school is that the pressure on the skate blade increases the melting point of ice which, in turn, produces liquid water which lubricates the skate.

Really? Let's plug a few figures in. Say the skate blade has a width of 1 mm and a length of 200 mm. This gives an area in contact with the ice of 200 mm^2, that is 0.32 in^2. Say the skater weighs 160 lb, that gives a pressure on the ice of about 500 psi, which is about 35 atm. Now, my ancient copy of Glasstone's Physical Chemistry gives a figure of 0.0075C per atm increase in the melting point of ice. So, 35 atm would increase the mp by a mere 0.26C, hardly enough to even notice.

I rest my case, m'lud.

Maggy
26-11-2003, 21:17
:knock:

oh give us a break.You wanna try teaching it to students who don't care. :cry:


incog. :sulk:

Ramrod
26-11-2003, 21:21
OK, while we're on the subject of ice, why can you easily skate on ice? . 'Cos it's slippery?:D