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Heat of atomization

  • #1
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Homework Statement


The heat of atomization of methane and ethane are 360kJ/moo and 620kJ/mol, respectively.
The longest wavelength of light capable of breaking the C-C bond is (Avogadro number = 6.02 x 1023, h= 6.62 x 1034J s

Homework Equations


E = hν = hc/λ

The Attempt at a Solution


I think we should consider energy of ethane only as it only has C-C bond.
What is the use of methane energy?
 

Answers and Replies

  • #2
Borek
Mentor
28,446
2,841
What bonds are present?
 
  • #3
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76
methane is CH4 and ethane is C2H6. All are single bonds.
 
  • #4
Borek
Mentor
28,446
2,841
Let me rephrase the question: bonds between what atoms are present?
 
  • #5
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76
Bonds between carbon and hydrogen are present in methane and in ethane between carbon and carbon and also carbon and hydrogen.
 
  • #6
Borek
Mentor
28,446
2,841
So you have two kinds of bonds. Methane contains only one kind, ethane contains two kinds. Within a good approximation bond energy doesn't depend on the molecule.
 
  • #7
1,007
76
So now what should I do?
Take E = 360 kJ/mol ?
 
  • #8
Borek
Mentor
28,446
2,841
360 kJ/mol is required to break how many bonds between which atoms? How much per this particular kind of bond is it?
 
  • #9
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76
To break 4 C-H bond we require 360 kJ. For 1 C-H bond it is 90 kJ.
For 6 C-H it is 540 kJ.
So for ethane, heat of atomization is 620 kJ.
So for C-C bond it is 90 kJ/ mol
For 1 C-C bond it is 90 / (6.02 x 1023) kJ
 
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  • #10
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18
Hi!!!
4 (C-H) bonds require 360kJ/mol....to break them
1×C-C bond+6(C-H) bonds require 620 KJ/mol.
So you can find C-C bond energy.
 
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  • #11
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Thanks all of you, got it.
Mooncrater I think we had written the posts at same time, so you don't realized my 9th post?
 
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  • #12
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18
Yup...you're absolutely right..heehee tech sometimes messes things up:)
 
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