So I am doing lots of studying for my GenChem I final next Wednesday. Surprisingly, stuff I didn't get before is now coming rather easily . One thing that I am confused about, though, is the following question:

 

What is the energy in joules of a mole of photons associated with visible light of wavelength 486 nm?

 

I know how to work it out and everything. When worked out, I get the answer 2.46 × 10-4 J. However, the answer marked correctly (I looked it up on the net, too) is 246kJ. Why is the answer in kJ even though it is asking for joules. This isn't so baffling as the fact that another question almost exactly like it has the correct answer in J.

 

Can anyone shed light on this? Thanks a bunch.

 

***Edit, one more thing. How come in the following question I have to multiply by avo's number when in the former one I had to divide?***

 

What is the energy in joules of a mole of photons associated with red light of wavelength 7.00 × 102 nm? (This answer actually comes out to joules, too)

 

Thanks again!

Edited December 8, 200916 yr by Marconis

For your first one I got 246kJ = 2.46 x 10^5 J, not 2.46 x 10^-4 J.

http://www.google.com/#hl=en&q=avogadro%27s+number+*+plank%27s+constant+*+c+%2F+486+nm&aq=f&aqi=&oq=&fp=be5ffa94030d2d34

 

On both of the questions you had to multiply by avogadro's number, to cancel out the mole "unit".

My fault, I didn't divide by avo's number in the first one...not sure why I thought I did. However, I still don't get why the answer is in kJ, when it is asking for J. And, like I stated, another very similar question (which I displayed) had the answer in J as opposed to kJ. It was literally the same question just different wavelengths.

 

Thanks

What do J measure? What do kJ measure?

k=1000x

Really sorry for wasting your time. I counted decimals incorrectly when looking at the answer in Joules, and it wasn't even a selection for an answer, which is why the correct one was in kJ. Disregard this entire thread.

 

Once again I apologize for my stupidity.

Eh, everyone eats a few zeros once in a while.

nom nom nom nom 0000000