Bustamove
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#1
Report Thread starter 7 years ago
#1
Hi, i'm currently doing AS and A2 chemistry AQA,
and i'm just wondering, how do you find enthalpy?

because in chem 2 (from the mark scheme), its
(delta) H = (sum of reactants) - (sum of products)

but in chem 4 or 5, it's
(delta) H = (sum of products) - (sum of reactants)

why are they different? how would you distinguish between the two? or is one of them wrong? help?
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anika1705
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#2
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#2
I have always learnt it the second way. I am currently doing OCR chemistry A. I have never calculated enthalpy using the first equation. Hope this helps.

(Original post by Bustamove)
Hi, i'm currently doing AS and A2 chemistry AQA,
and i'm just wondering, how do you find enthalpy?

because in chem 2 (from the mark scheme), its
(delta) H = (sum of reactants) - (sum of products)

but in chem 4 or 5, it's
(delta) H = (sum of products) - (sum of reactants)

why are they different? how would you distinguish between the two? or is one of them wrong? help?
0
reply
Bustamove
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#3
Report Thread starter 7 years ago
#3
(Original post by anika1705)
I have always learnt it the second way. I am currently doing OCR chemistry A. I have never calculated enthalpy using the first equation. Hope this helps.
i calculated it using the second way in a chemistry unit 2 paper and the mark scheme said it was wrong....
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Bustamove
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#4
Report Thread starter 7 years ago
#4
I'm doing the chem unit 2 paper here:
http://filestore.aqa.org.uk/subjects...W-QP-JAN10.PDF

question 1 d)
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anika1705
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#5
Report 7 years ago
#5
(Original post by Bustamove)
I'm doing the chem unit 2 paper here:
http://filestore.aqa.org.uk/subjects...W-QP-JAN10.PDF

question 1 d)
I took a look at the question and the mark scheme and I think that the mark scheme is wrong. It should be products - reactants. I think the best thing to do would be ask to ask your teacher. They will definitely provide you with the right answer
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mynameisntbobk
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#6
Report 7 years ago
#6
I thought for bond enthalpies, it was bonds broken - bonds formed
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