[LMB] How demons work: what happened to the heat energy?
baur at chello.at
Wed Aug 3 19:21:50 BST 2016
that IS an interesting question
request - someone please check my chemistry and arithmetic - it has been
some time since i last did this ..
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 kJ / g / °C (for the liquid phase)
so the energy release of the rusting dagger is sufficient to change the
temperature of 393 grams of water (a bit more then 1/3 of a liter) by
one degree Celsisus - 1644 / 4,186 = 392,74
not very much ... that energy release might not even be noticed in the
"heat of battle" if it is directed somewhere "else" 8)
Am 30.07.2016 um 01:14 schrieb Matthew George:
> Okay, Rusilin tries to stab Penric in the stomach with a knife, and the
> blade turns to rust so rapidly the stabbing fails.
> What happened to all the heat energy that should have been released?
> Matt "interesting..." G.
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Am 03.08.2016 um 20:18 schrieb markus baur:
> yes - but does it run on oxydising iron? or on something more energetic?
> i posted the energy calculation for the dagger rusting a few days ago -
> did anyone check the arithmetic and chemistry?
> Am 03.08.2016 um 18:14 schrieb Matthew George:
>> I'm currently looking at one of those heating packets intended to warm
>> people's gloves and suchlike in winter. It's less weighty than I'd
>> the blade of a dagger to be, and under normal operating conditions it's
>> stated to be able to reach 155 degrees Fahrenheit. Used improperly I
>> they can set things on fire.
>> Lois-Bujold mailing list message sent to baur at chello.at
>> Lois-Bujold at lists.herald.co.uk
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