Omg this is driving me crazy.. energy calculation question Watch

lil_dreamer90
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Hi all, arghh im so confused i just dont get this question! Its OCR salters and the question is in June 2005 module 2850, question 2 if anyone is looking at it.

they say :
calculate the maximum enery that could be relased from burning this mass of coal. asssume that coal is pure carbon

enthalpy change of combustion = -394 kJ per mol

on the prevoius part of the question they gave a table saying starting mass of coal in grams is 20 and finishing mass is 18.80 ( the other part of the question was calculate the energy transferred to the water by the mass of coal burned)

what are they asking for here? it is energy density or something else?

anyones help is appreciated - thank uuu

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lil_dreamer90
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ok i just had a breakthrough- i think i get it now!! do you just find the no. of moles and then times it by enthalpy change of combustion to get the maximum energy transferred? i got the right answer - am i right in using this method?

i used the conversion:

energy transfered = ethalpy change of combustion (by dividing no.of moles)
ethalpy change combustion = energy transferred (by times no. of moles)
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psychic_maniac
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yeh, you work out the number of moles of coal that you've burnt and multiply it by the enthalpy change of combustion per mole
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gem1256
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(Original post by lil_dreamer90)
ok i just had a breakthrough- i think i get it now!! do you just find the no. of moles and then times it by enthalpy change of combustion to get the maximum energy transferred? i got the right answer - am i right in using this method?

i used the conversion:

energy transfered = ethalpy change of combustion (by dividing no.of moles)
ethalpy change combustion = energy transferred (by times no. of moles)
im working though past papers right now, but i don't have the markscheme for this one. If you have it is there any chance you could get it to me.
Thanks, good luck in tomorrows exam (if you have it then)
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