[Chemistry A2] Diatomic molecules in Born Haber cycles

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itslibster
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I've been working pretty well with born Haber cycles and I can draw them out fine but when it comes to the calculations I'm stumped with diatomic molecules.

It comes really to molecules like Cl2(g)--> 2Cl(g) or 1/2 Cl2(g)--> Cl (g) with bond dissociation and atomisation.

When is it appropriate to halve or double given values for enthalpy of atomisation or dissociation?

Examples
1) 1/2 F2(g) --> F(g)
2) F2(g)--> 2F(g)
(enthalpy of atomisation of fluorine= +79kj/mol)


Where is it halved or doubled? this is definitely the part I fall down on lol. also, what is the difference between bond dissociation and atomisation when it comes to diatomic molecules??
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charco
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(Original post by itslibster)
I've been working pretty well with born Haber cycles and I can draw them out fine but when it comes to the calculations I'm stumped with diatomic molecules.

It comes really to molecules like Cl2(g)--> 2Cl(g) or 1/2 Cl2(g)--> Cl (g) with bond dissociation and atomisation.

When is it appropriate to halve or double given values for enthalpy of atomisation or dissociation?

Examples
1) 1/2 F2(g) --> F(g)
2) F2(g)--> 2F(g)
(enthalpy of atomisation of fluorine= +79kj/mol)


Where is it halved or doubled? this is definitely the part I fall down on lol. also, what is the difference between bond dissociation and atomisation when it comes to diatomic molecules??
Decide on how many atoms you need and use:
Enthalpy of atomisation makes 1 mol of atoms
Bond enthalpy breaks 1 mol of bonds and makes 2 mol of atoms
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itslibster
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(Original post by charco)
Decide on how many atoms you need and use:
Enthalpy of atomisation makes 1 mol of atoms
Bond enthalpy breaks 1 mol of bonds and makes 2 mol of atoms
thanks! So for example 1 it's atomisation and the number remains the same, but for example 2 it's bond dissociation? If I was given the atomisation enthalpy and example 2, I'd double the value right?
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charco
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(Original post by itslibster)
thanks! So for example 1 it's atomisation and the number remains the same, but for example 2 it's bond dissociation? If I was given the atomisation enthalpy and example 2, I'd double the value right?
yes
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