Light that has enough energy to cause this bond to break?

[jewilki1]

I really need help with this problem. I need to know how to work it and the answer. I am trying to review all these problems and they do not have answers.
2. It requires 242.7 kJ/mol to fragment Cl2 molecules into Cl atoms. What is the longest wavelength (in nanometers) of light that has enough energy to cause this bond to break?

Could you please explain this to me? I have the answer: 242.7 kJ/mol. Is this right?

Thanks.

 

[sanitykey]

To find the energy required to cause one bond to break you would have to divide the energy that is given for one mol of Cl_{2} molecules to fragment into Cl atoms by the number of Cl_{2} molecules in one mol. There are 6.02 \times 10^{23} Cl_{2} molecules in one mol.

Then when you've found this amount of energy you can find the photon wavelength required to produce it by using the equation:

\lambda = \frac {E \times c}{h}

Where \lambda is the longest wavelength required to fragment the molecules as the calculation assumes no energy is lost, E is the energy of the photon, c is the speed of light (about 3 \times 10^8) and h is Planck's constant (6.63 \times 10^{-34}).