# Heat of atomization

1. Apr 20, 2015

### Raghav Gupta

1. The problem statement, all variables and given/known data
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

2. Relevant equations
E = hν = hc/λ
3. 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?

2. Apr 20, 2015

### Staff: Mentor

What bonds are present?

3. Apr 20, 2015

### Raghav Gupta

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

4. Apr 20, 2015

### Staff: Mentor

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

5. Apr 20, 2015

### Raghav Gupta

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

6. Apr 20, 2015

### Staff: Mentor

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. Apr 20, 2015

### Raghav Gupta

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

8. Apr 20, 2015

### Staff: Mentor

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

9. Apr 20, 2015

### 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

10. Apr 20, 2015

### 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.

11. Apr 20, 2015

### 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?

12. Apr 20, 2015

### mooncrater

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