[alocheim]

The problem states: A common way of initiating certain chemical reactions iwth liht involves the generation of free halogen atoms in solution.  I the change in enthalpy for the reaction Cl2-->2Cl is 242.8 kJ/mol, what is the longest wavelength of light that will produce free chlorine atoms in solutions?

If someone could give me a jumping off point, I would really appreciate it.  I've been trying to figure this one out for awhile and cannot seem to come up with the correct answer.

[Fluorine]

You are given energy required (E) and you need wavelength (λ, lambda).

See if rearranging this will give you the answer;



where E is energy, h is Planck constant, c is the speed of light, and lambda is wavelength.

[alocheim]

Thanks for taking a look, but I have figured this one out finally. I was making a very simple error that was throwing off my answer.  If anyone else is having trouble with a similar problem, this is how I came to my answer:

Quick note--I had not originally given that the Cl2 and 2Cl were in the gaseous state.

To solve, I first converted my  :delta:H/mol to J/atom and used this energy as the work function.  Then I just plugged in the numbers and solved for wavelength by rearranging the equation w= h * (frequency), which gives:

[lambda] = (c*h)/w  

Then all that was left was to convert from m to nm.

[alocheim]

Thanks Flourine.  In my sleepiness, I kept using 6.22 x 10^23 in my conversions

[Fluorine]

Glad to hear you've figured it out then.