Heat combustion of ethanol...

[Casmira]

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Im revising my chem stuff and when i started on ethanol as a fuel combustion calculations i was in conquering chem and got stuck on this chem (pg 32 q30 for those who have the book)
help would be great thanks in advance!

The heat combustion of ethanol is 1360 kJ/mol. What mass of ethanol needs to be burnt to raise the temperature of 350 g of water through 77 degrees selcius, if 50% of the heat released by ethanol is lost to the surroundings? the specific heat capacity of water is 4.2J K-1 g-1

the answers 7.7g

[theChemCoach]

Casmira,

Its excellent to see you are having ago at this question.
It is not difficult once you have mastered the basic concepts.

I have attached the solution to the question, it is a very exhaustive solution, as i try to explain every step.
Most steps (prob half the working), with good time and practice you will be able to do in your head.

Any questions, post them here, or even better discuss the solution with your class teacher at school.
This way he will be able to explain any of the concepts you have trouble with.

Cheers,
George


Get Solution Here.........

[Casmira]

Shit! Thanks so much for that youre a champ

I was too fooling around with the molar mass of ethanol, then i did 46/6 = 7.6 repeater
my little mthod worked with another question as well, when i get the chance ill scan up what my owrking out was, but damn your method makes more sense

i did this

= 1360 / 113.19
= 12.015...
= 12.015/2 (because half of it is "lost")
= 6.0075...
= 46/6.0075...
= 7.65

this method also worked with another question i found on conq chem website, but think ill get the wrong answer for marking out