born haber cycle question help Watch

Bertybassett
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Hi, for question 3cii on this paper, I got 140, yet in the ms it seems to include 289 in the calculation yet in the table it says 298? I cant tell if the ms is just wrong or not? thanks https://pmt.physicsandmathstutor.com...s%201%20QP.pdf
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MrMoment
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Remember, when considering fluorine- bond dissociation enthalpy is double atomisation enthalpy:

Atomisation:
1/2F2(g) -> F(g)

Bond dissoc:
F2(g) -> 2F-(g)

The difference between your answer and the MS being roughly a factor of 2 makes me think that this could be your error.
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Bertybassett
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I mean I got an answer of 140 but the ms gets a different answer. I dont get what they've done in the ms. Also, the answer in the ms wasn't 298, I was just saying within the calculation should have 298 but the ms used 289.

Also, in the equation for bond dissociation, why is it 2f-(g) and not 2f(g)? Why are they ions?
(Original post by MrMoment)
Remember, when considering fluorine- bond dissociation enthalpy is double atomisation enthalpy:

Atomisation:
1/2F2(g) -> F(g)

Bond dissoc:
F2(g) -> 2F-(g)

The difference between your answer and the MS being roughly a factor of 2 makes me think that this could be your error.
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hassan1236945
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Yep just realised the MS uses 289 not 298 so it must be a typo. Just did it using the questions numbers and got (70*2)
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Bertybassett
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yeah that's what I got too. thanks for the help
(Original post by hassan1236945)
Yep just realised the MS uses 289 not 298 so it must be a typo. Just did it using the questions numbers and got (70*2)
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