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Homework Help: Dissociation energy ?

  1. Oct 13, 2008 #1
    1. The problem statement, all variables and given/known data

    The spectroscopic dissociation energy of 127-I2 is 1.542eV. What wavelength of light would be needed to dissociate the molecule and have the atoms move apart at velocities of 1000 m/s?

    2. Relevant equations

    3. The attempt at a solution

    What I did was convert 1.542eV to joules which became 2.47x10^-19 joules/mol. After that I found the total energy per bond by dividing the energy be avagadro's number = 4.1x10^-43. Then plugged it into wavelength = hc/E = 4.8x10^17m. But this didn't look right. Am I going about it the wrong way? Or should I just go straight to wavelength = hc/E using the 1.542eV to find the wavelength. Or work backwards using KE=1/2 mv^2?

    Thanks in advance
  2. jcsd
  3. Oct 14, 2008 #2


    User Avatar

    Staff: Mentor

    1.542 eV is energy required for 1 molecule to be dissociated. However, your light must carry more energy, as the atoms need kinetic energy.
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