# Ionization energy and wavelength problem

• Dec 6th 2011, 12:01 PM
Hamzawesome
Ionization energy and wavelength problem
I can't figure this problem out, despite using E = hc/lambda...

The first ionization energy for potassium in the vapor state is 418.8 kJ/mol. Determine the longest wavelength that could be used to ionize an atom of potassium.
• Dec 6th 2011, 01:40 PM
e^(i*pi)
Re: Ionization energy and wavelength problem
Quote:

Originally Posted by Hamzawesome
I can't figure this problem out, despite using E = hc/lambda...

The first ionization energy for potassium in the vapor state is 418.8 kJ/mol. Determine the longest wavelength that could be used to ionize an atom of potassium.

$E = \dfrac{hc}{\lambda}$ only works for individual molecules. You need to find a scale factor between moles and molecules (think Avogadro) and watch the units, E in that equation is in joules whereas your value is in kJ

edit: I get an answer of 285.6nm