[LMB] How demons work: what happened to the heat energy?

markus baur baur at chello.at
Wed Aug 3 19:21:50 BST 2016


resending:

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)

servus

markus


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.
 > --
 > Lois-Bujold mailing list message sent to baur at chello.at
 > Lois-Bujold at lists.herald.co.uk
 > http://lists.herald.co.uk/cgi-bin/mailman/listinfo/lois-bujold
 >


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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?
>
> servus
>
> markus
>
> 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
>> expect
>> 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
>> know
>> they can set things on fire.
>> --
>> Lois-Bujold mailing list message sent to baur at chello.at
>> Lois-Bujold at lists.herald.co.uk
>> http://lists.herald.co.uk/cgi-bin/mailman/listinfo/lois-bujold
>>
>
>


-- 
markus baur                     SCA: markus von brixlegg
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a-1040 wien                     email: baur at chello.at
austria/europe                  icbm: 48°11'39"N; 16°22'06"E

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