# Born haber cycle help

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Thread starter 1 day ago
#1
So i have my chemistry exam in a few hours and i’m confused. When we measure the enthalpy of atomisation of e.g chlorine and it goes cl2>>2cl do we do enthalpy of atomisation times by 2 and with 1/2cl2>Cl what would that be. I’m seeing different things in my notes and in the past paper i’ve done. Also electron affinity of its 2Cl would be 2 x electron affinity right?
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1 day ago
#2
no you don't times by 2 when you go from half to 1 for this
you only times 2 when u get the 2 infront of anything i'd double check with someone else though ! i'm a little confused with this myself
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Thread starter 1 day ago
#3
(Original post by bugaboo02)
no you don't times by 2 when you go from half to 1 for this
you only times 2 when u get the 2 infront of anything i'd double check with someone else though ! i'm a little confused with this myself
Thanks i’ll email my teacher hopefully he replies
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1 day ago
#4
(Original post by mxx454)
So i have my chemistry exam in a few hours and i’m confused. When we measure the enthalpy of atomisation of e.g chlorine and it goes cl2>>2cl do we do enthalpy of atomisation times by 2 and with 1/2cl2>Cl what would that be. I’m seeing different things in my notes and in the past paper i’ve done. Also electron affinity of its 2Cl would be 2 x electron affinity right?
This is precisely why you need to learn the enthalpy definitions!

The enthalpy of atomisation is per mole of atoms formed
So, yes, you do need to multiply by 2.

If you are given the bond enthalpy of chlorine, it would be different. 1 mole of bonds makes 2 moles of atoms.
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Thread starter 1 day ago
#5
(Original post by charco)
This is precisely why you need to learn the enthalpy definitions!

The enthalpy of atomisation is per mole of atoms formed
So, yes, you do need to multiply by 2.

If you are given the bond enthalpy of chlorine, it would be different. 1 mole of bonds makes 2 moles of atoms.
Oh right that makes sense thank you. I’m a little confused with the bond enthalpy though. Like how would they give bond enthalpy in the question, is it the same as Cl2>>2Cl
Last edited by mxx454; 1 day ago
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1 day ago
#6
(Original post by mxx454)
Oh right that makes sense thank you. I’m a little confused with the bond enthalpy though. Like how would they give bond enthalpy in the question, is it the same as Cl2>>2Cl
The bond enthalpy definition is the energy required to break one mol of specified bonds in a gaseous substance.

Cl2(g) ==> 2Cl(g) ΔH = +242 kJ

This is equal to double the enthalpy of atomisation
Last edited by charco; 1 day ago
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Thread starter 1 day ago
#7
(Original post by charco)
The bond enthalpy definition is the energy required to break one mol of specified bonds in a gaseous substance.

Cl2(g) ==> 2Cl(g) ΔH = +242 kJ

This is equal to double the enthalpy of atomisation
Oh thank you sm
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