[LMB] How demons work: what happened to the heat energy?
baur at chello.at
Wed Aug 3 21:16:03 BST 2016
Am 03.08.2016 um 21:43 schrieb Matthew George:
> The heat packs' ingredients are oxidizing iron, some fillers, and catalysts.
> I do wish you wouldn't switch back and forth between decimal points and
> commas. Very misleading to casual reading.
thats what i get when i try to cater to the english 8) .. i am used to
commas - the point is for me the deliniation for 10^3
> Isn't the heat capacity of water approximately 4.184 *J* per gram degree
> celsius, not *kJ*? I think that would make your answer off by a factor of
> a thousand.
i just checked - and you are right, i am off by 10^3
i read 4.184 as four thousand one hundred and something (or 4.something
kilo) - with the point delineating the 10^3
this is exactly why i was asking to check me 8)
corrected version - but please keep checking - and i changed all commas
and the correction changes the reults a lot ..
the enthalpy of of Fe to Fe2O3 (main constituent of rust) is 822 kJ/mol
lets say this is a lightweight stabbing dagger weighing 111 gram (only
the iron parts)
one mol of Fe is 55,845 gram - so the dagger equals 2 mols of iron ..
total energy release is 1644 kJ
the specific heat of water is:
4.186 J / g / °C (for the liquid phase)
so the energy release of the rusting dagger is sufficient to change the
temperature of 393000 grams of water (about 393 liter) by
one degree celsisus - 1644 / 4.186 = 392.74
or change the temperature of 80kg of water (one human adult's worth) by
about 4.9°C - and THAT change would be very noticable as it would raise
the body temperature into lethal ranges, if you could distribute it evenly
or it would boil about 4 to 6 liters of water (depending on the starting
temperature of the water) - again very noticeable
but nothing like these effects were reported
so we have to ask where all that energy goes ..
> Matt G.
> Lois-Bujold mailing list message sent to baur at chello.at
> Lois-Bujold at lists.herald.co.uk
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