Naked Science Forum

General Science => General Science => Topic started by: neilep on 06/03/2012 00:19:45

Title: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: neilep on 06/03/2012 00:19:45
Dearest Bags Of Mostly Eau,

As a Sheepy I of course luff water !..Water is my all time favourite transparenty type neutral tasting liquid thing that is best served cool. I prefer to dilute mine !. .......Water was invented in 1577 by Sir Francis Drake so that he could circumnavigate the Earth in his boatmobile that he had just invented the year before !


Look, here's some !

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Diluted Water (1 parts water to 2 parts water)


Hmmm...nice eh ?


Ok..Ok....listen up !!....In apparent contradiction to the topic title cold water is denser than hot water (at temps above 4C) . This is something to do with things called molecules that roam around in packs and are really quite tight together when it's brrrrrrrrrrrrrrr cold !!...so here's the weird thing !!......If ewe took a sealed bottle of water at 100c and then let it cool down to 4c the mass actually drops !!...????????


Why's that then ? Why  Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4C ?



Water is like....well weird in certain properties eh ?


whajafink ?...can ewe help splain it to me ?


hugs and shmishes


mwah mwah mwah




neil
Sir Francis Drake
Also Invented The Lake
xxxxxxxxxxxxxxxxxxx



Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: RD on 06/03/2012 02:30:47
Why  Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4C ?

The mass does not change, but the volume does: if it was exactly a litre at 100C, the volume of water would be a little less than a litre when it cooled, because as you said colder water is denser than hot.

BTW don't try this gedankenexperiment for real: a sealed container of water heated from 20C to 100C could explode, an open container heated to 100C then sealed could implode when cooled ...
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: damocles on 06/03/2012 10:02:46
(1) You can safely try the second part of the experiment; A glass bottle should be quite safe to withstand an external pressure of 1 atm, or a PET bottle can flex easily to reduce its internal volume. So cooling from 100 to 4 is safe. Heating from 4 to 100 might break the bottle, but unless the temperature was taken above 100 (or, rather, the local boiling point of water, which may well be several degrees lower depending on your location) it would do so via gentle cracking, not in an explosion. Definitely use cooling mode rather than heating mode.

(2) If you actually try the experiment, and if you do not know much about accurate mass determination, then the hot water will appear to be heavier. On the face of it a sealed bottle at 100C should appear to weigh less on the balance pan, because it will be displacing a larger mass of air. This effect is minute. I think that an even more important factor will be an upward convection current of hot air rising from contact with the hot bottle, which will produce an equal and opposite downward force on the balance pan, and the appearance of increased weight.
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: neilep on 06/03/2012 11:56:27
Why  Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4C ?

The mass does not change, but the volume does: if it was exactly a litre at 100C, the volume of water would be a little less than a litre when it cooled, because as you said colder water is denser than hot.

BTW don't try this gedankenexperiment for real: a sealed container of water heated from 20C to 100C could explode, an open container heated to 100C then sealed could implode when cooled ...

Thanks RD for clarifying that for me. I'm sure I heard the contrary but that's why I'm asking the question.  TA !
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: CZARCAR on 06/03/2012 20:08:58
E=MC2 SO E+1=[M+1]C2?
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: neilep on 07/03/2012 05:04:40
E=MC2 SO E+1=[M+1]C2?

Does this prove my original question ? (I'm a novice here..I do recognise an Einstein thing but my abacus can't calulate the rest ! [:-[])
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: damocles on 07/03/2012 05:26:15
neilep, you need one of those new-fangled abaci with an alphabetic keyboard. But calulation is a dangerous pursuit anyway (as opposed to calculation).
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: Sprool on 08/03/2012 10:39:57
Whilst circumventing the Plimsol line, Sir Francis Einstein discovered that water at 10C has a density of approx 999.7g/l, whilst on heating up to 99C, the density reduced to 958.4g/l. This makes good sense when you visualise all those extra energy water molecules dashing about everywhere bumping into stuff.
Thus that eveng he mused that hot bottles of fixed volume would have nearly 4% less mass liquid in it than a cold one even though he hadn't accounted for thermal expansion coefficient. From this was derived the invention of the potato which strangely has almost exactly the same density as his own head.
I rest my case.
Title: Re: Why Does A Litre Of 100C Water Have MORE Mass Than When The Water Cools To 4c ?
Post by: Cheese2001 on 17/03/2012 04:24:51
If the mass decreases with temperature, we may have to reconsider the "Law of Conservation of Mass."