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Homework Help: Calculte the Energy of 1 mole of photons - Help

  1. Oct 25, 2008 #1
    Calculte the Energy of 1 mole of photons - Help!!!

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

    Calculate the energy, in kilojoules, of one mole of photons of yellow laser light of wavelength 570 nm.

    The correct answer is: 2.10x102

    2. Relevant equations
    Ephoton= hc/wavelength


    3. The attempt at a solution


    Step by step:
    1. Convert the wavelength of 570nm to m:

    10-9m= 1 nm, so:

    570nm * (10-9m) = 5.7E-7 m

    2. Ephoton= hc/wavelength

    Ephoton= (6.63E-34 * 3.E8)/5.7E-7 m

    Ephoton= 3.49E-19 J

    3. Finally, I convert to kJ:

    Ephoton= 3.49E-19J/1000J = 3.49E-22 kJ

    Can someone help me with this problem, I tried many times but I still get the same result.
     
  2. jcsd
  3. Oct 26, 2008 #2

    rock.freak667

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    Re: Calculte the Energy of 1 mole of photons - Help!!!

    Think of Avogadro's number/constant.
     
  4. Oct 26, 2008 #3
    Re: Calculte the Energy of 1 mole of photons - Help!!!

    So, I would have:
    3.49E-22 kJ * the Avogadro's constant, which is 6.022 × 10E23 mol-1
    And I got the answer. yoohoo! Thank you so much. Please explain to me why I have to multiply my answer with the Avogadro's constant to get the final answer. I appreciate your help!
     
  5. Oct 26, 2008 #4

    rock.freak667

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    Re: Calculte the Energy of 1 mole of photons - Help!!!

    One mole should contain 6.02E23 elementary units. You found the energy of 1 elementary unit.
     
  6. Oct 26, 2008 #5
    Re: Calculte the Energy of 1 mole of photons - Help!!!

    Oh, I forgot that concept. Thanks for reminding me. One mole of any substance contains this many [6.022 × 10E23] units. :D Cheers!
     
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