Some chem homework, I see the answer, but how did they get it?

[Mr Bob]

I am wondering abbout question 5 here > http://www.colorado.edu/chemistry/chem1111/TutorialCH6&7.pdf

I don't see how they derived at the answer.

I figured there would be a few people here that could explain it.

 

[Howard]

Don't remember my formulas, sorry.

 

[Mr Bob]

I have some here:

E=hv

h=6.626x10^-34
v=frequency
c=3.00x10^8 m/s

E= (hc)/(wavelength)

wavelength=(h)/(mass in kg)(velocity)

 

[Darien]

What is the energy of 1 photon?

What is the total energy in 1 second, noting the 12% efficiency?

 

[da loser]

at least post the question you lazy bastard

 

[Mr Bob]

" What is the energy of 1 photon?"
- Isnt that what I need to figure out, it will be that times the number of J/s I believe.

"What is the total energy in 1 second, noting the 12% efficiency?"
- 12% of 105, which is 12.6

"at least post the question you lazy bastard"
- It looks much nicer in the PDF form. If someone is going to take their time to try and help with the problem, they are going to be fine with clicking a single link to make the question/answer in a very nice format.

 

[Splork]

I hope you don't need this soon. I'm going to work on it later after I get back from being out tonight. Good luck.

-sp

 

[TuxDave]

Originally posted by: Mr Bob
" What is the energy of 1 photon?"
- Isnt that what I need to figure out, it will be that times the number of J/s I believe.

"What is the total energy in 1 second, noting the 12% efficiency?"
- 12% of 105, which is 12.6

"at least post the question you lazy bastard"
- It looks much nicer in the PDF form. If someone is going to take their time to try and help with the problem, they are going to be fine with clicking a single link to make the question/answer in a very nice format.

12.6J/s = "X" photons/sec * "Y" J/photon

Solve for X given that you can calculate Y.

 

[Mr Bob]

I just want to "learn" how to do it. I'll be back in 10 minutes, it seems like Dave is on something here. Ill be back and see how it goes.

 

[Mr Bob]

And thanks to Dave, here is how you solve it.

Since 12.6J/s = "X" photons/sec * "Y" J/photon

And we are looking for photons/sec, we find that:
(photons/sec)=(J/s)/(J/photon)

J/s = 105 watts * efficiency = 12.6

J/photon = (c*h)/(wavelength in meters)

c = 3.00x10^8 m/s
h = 6.626x10^-34
wavelength in meters = 1.525 x 10^-6

Thus J/photon = ((3.00x10^8 m/s)*(6.626x10^-34))/(1.525 x 10^-6) = 1.303 x 10^-19

Since:
J/s = 12.6 and
J/photon = 1.303 x 10^-19

and (photons/sec)=(J/s)/(J/photon)

Then (photons/sec) = 12.6/1.303 x 10^-19