Heat of Atomization Ethane: Wavelength to Break C-C Bond

[Raghav Gupta]

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?

 

[Borek]

What bonds are present?

 

[Raghav Gupta]

methane is CH4 and ethane is C2H6. All are single bonds.

 

[Borek]

Let me rephrase the question: bonds between what atoms are present?

 

[Raghav Gupta]

Bonds between carbon and hydrogen are present in methane and in ethane between carbon and carbon and also carbon and hydrogen.

 

[Borek]

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.

 

[Raghav Gupta]

So now what should I do?
Take E = 360 kJ/mol ?

 

[Borek]

360 kJ/mol is required to break how many bonds between which atoms? How much per this particular kind of bond is it?

 

[Raghav Gupta]

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

 

[mooncrater]

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.

 

[Raghav Gupta]

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?

 

[mooncrater]

Yup...you're absolutely right..heehee tech sometimes messes things up:)