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Topic: Born Haber cycle help  (Read 815 times)

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Offline lush_xx

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Born Haber cycle help
« on: July 23, 2022, 12:11:20 AM »
hello all

i am finding it hard to enter the values for this born haber cycle with a given group of values can someone show me how its done please?

after using a youtube tutorial this is what i calculated:

A =737
B = 400
C = 200
D= 200
F = -1765

but i dont know if it is right

please look at the attachment

Offline Borek

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Re: Born Haber cycle help
« Reply #1 on: July 23, 2022, 06:35:54 AM »
How is the enthalpy of formation defined? Can you write reaction equation for the formation of MgX2(s)?
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Offline lush_xx

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Re: Born Haber cycle help
« Reply #2 on: July 23, 2022, 06:55:17 AM »
How is the enthalpy of formation defined? Can you write reaction equation for the formation of MgX2(s)?

I am not too certain the image is a practice question i found online, most youtube videos I watched doesnt seem to cover this type of born haber question

Offline lush_xx

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Re: Born Haber cycle help
« Reply #3 on: July 23, 2022, 06:59:41 AM »
How is the enthalpy of formation defined? Can you write reaction equation for the formation of MgX2(s)?
Mg+X2 = MgX2 ?

Offline Borek

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Re: Born Haber cycle help
« Reply #4 on: July 23, 2022, 08:07:16 AM »
Your reaction equation misses states - add them and compare the reaction you wrote with the reactions D and F. Which one is it?
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Offline lush_xx

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Re: Born Haber cycle help
« Reply #5 on: July 23, 2022, 09:20:06 AM »
I don't get it, how to I know where to input the values given

Offline Borek

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Re: Born Haber cycle help
« Reply #6 on: July 23, 2022, 11:45:31 AM »
Large part of what you did is OK, but not everything.

Which of the processes - D or F - is a formation of the MgX2(s)? How is the formation defined?
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Offline lush_xx

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Re: Born Haber cycle help
« Reply #7 on: July 23, 2022, 12:17:11 PM »
I think D would be the formation as it has mgx2(s)

Offline lush_xx

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Re: Born Haber cycle help
« Reply #8 on: July 23, 2022, 12:19:11 PM »
Large part of what you did is OK, but not everything.

Which of the processes - D or F - is a formation of the MgX2(s)? How is the formation defined?
as D is formation perhaps the value  is -450 but I dont know how to calculate the other boxes with just this figure

Offline Borek

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Re: Born Haber cycle help
« Reply #9 on: July 23, 2022, 01:31:41 PM »
I will ask for the third time: please quote the definition of the formation enthalpy.

As long as you ignore what you are being asked we won't move forward.
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Offline lush_xx

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Re: Born Haber cycle help
« Reply #10 on: July 23, 2022, 01:53:20 PM »
I will ask for the third time: please quote the definition of the formation enthalpy.

As long as you ignore what you are being asked we won't move forward.

change of enthalpy where 1 mole of a particular element is formed from their component in their standard form?

Offline Borek

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Re: Born Haber cycle help
« Reply #11 on: July 23, 2022, 01:56:42 PM »
in their standard form?

What is the standard form for Mg and for X?

Hint: Mg(s) or Mg2+(g)?
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Offline lush_xx

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Re: Born Haber cycle help
« Reply #12 on: July 23, 2022, 01:58:52 PM »
in their standard form?

What is the standard form for Mg and for X?

Hint: Mg(s) or Mg2+(g)?
Mg(s) as it is at the bottom of the cycle

Offline Borek

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Re: Born Haber cycle help
« Reply #13 on: July 23, 2022, 03:38:06 PM »
Mg(s) as it is at the bottom of the cycle

No, it is not because it is at "the bottom of the cycle", standard states are defined: https://en.wikipedia.org/wiki/Standard_state

But yes, Mg(s) is the standard state. So, if the Mg(s) is a standard state, and the formation enthalpy is formation from standard state, which process - D or F - is the formation of MgX2(s)?

Once you assign correctly enthalpy of the formation of MgX2(s) to one of the processes in the cycle it will be obvious what is left to calculate - and it should be also obvious how to calculate it.
« Last Edit: July 23, 2022, 04:28:52 PM by Borek »
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Offline Aldebaran

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Re: Born Haber cycle help
« Reply #14 on: July 24, 2022, 06:29:16 AM »
Together with Borek's coaching, the following link may help you: https://www.chemguide.co.uk/physical/energetics/lattice.html

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