Photoionization and First Ionization Energy

[MDwannabe7]

Photoionization is apparently a good method to measure first ionization energies conveniently given the equation I=hv where I is ionization energy, h is Planck's constant and v is the frequency of light absorbed. Sodium has a first ionization energy of 496kJ/mol. What is the frequency of light absorbed per photon in the photoionization of a gas phase sodium sample?

Since I=hv, then 496 kJ/mol = 6.63x10^-34 Js * v

So all I should have to do is divide 496 kJ/mol by 6.63x10^-34 Js to get v and that should be my answer, right?

Well, I got 7.48x10^38 Hz and the answer is really 1.24x10^15 Hz.

Where did I go wrong?

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[Soccerdoc11]

Photoionization is apparently a good method to measure first ionization energies conveniently given the equation I=hv where I is ionization energy, h is Planck's constant and v is the frequency of light absorbed. Sodium has a first ionization energy of 496kJ/mol. What is the frequency of light absorbed per photon in the photoionization of a gas phase sodium sample?

Since I=hv, then 496 kJ/mol = 6.63x10^-34 Js * v

So all I should have to do is divide 496 kJ/mol by 6.63x10^-34 Js to get v and that should be my answer, right?

Well, I got 7.48x10^38 Hz and the answer is really 1.24x10^15 Hz.

Where did I go wrong?

Don't forget that it is asking the frequency of light absorbed PER PHOTON.. They give you 496 KJ/mol so just use Avogadro's # (6.02 X 10^23/mole) to get the energy per photon. Then just divide by Planck's constant and you should get the answer you provided (if my math was correct). Hope that helps.. O yeah also it is in KJ , have to convert it to Joules.

 

[MDwannabe7]

Thanks - that helps - I always forget about good ole Avogadro - hopefully I remember to remember him come late August...