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Hess's Law - enthalpy change question

So I know it all adds up +344 ----> +350.

But how is -3 the answer? Why is it overall divided by 3?

Thanks :smile:
Screen Shot 2016-06-05 at 18.48.51.png47.6KB
Original post by _Lizabeth_
So I know it all adds up +344 ----> +350.

But how is -3 the answer? Why is it overall divided by 3?

Thanks :smile:


The question can't be answered without the enthalpy of vaporisation of both bromine and iodine ...
Reply 2
Avatar for _Lizabeth_
_Lizabeth_
OP
15
Original post by charco
The question can't be answered without the enthalpy of vaporisation of both bromine and iodine ...


This is the answer, I just want to know why it's /2
Screen Shot 2016-06-06 at 14.42.05.png19.8KB
Original post by _Lizabeth_
This is the answer, I just want to know why it's /2


The enthalpy of formation only requires 1/2 mole of each of the halogens....
Original post by _Lizabeth_
So I know it all adds up +344 ----> +350.

But how is -3 the answer? Why is it overall divided by 3?

Thanks :smile:


0.5 I2 + 0.5 Br2 --> 1 IBr
Formation infers 1 mole (enthalpy of formation)
Reply 5
Avatar for mors13
mors13
10
i know its very late, but just in case anyone else who finds this needs help,
0.5 Br2 + 0.5 I2 → IBr
enthalpy change = 0.5(193) + 0.5 (151) - 175 = -3
(edited 3 years ago)
Reply 6
Avatar for txxxx
txxxx
1
Original post by mors13
i know its very late, but just in case anyone else who finds this needs help,
0.5 Br2 + 0.5 I2 → IBr
enthalpy change = 0.5(193) + 0.5 (151) - 175 = -3

why divide by 0.5

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