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Sapling Homework - electron affinity

Posted: Thu Oct 22, 2020 8:12 pm
by SamanthaTolentino 3D
The electron affinity of thulium has been measured by a technique known as laser photo-detachment electron spectroscopy. In this technique, a gaseous beam of the anions of an element is bombarded with photons from a laser. Electrons from the anion are then ejected and their energies are detected. The incident radiation is had a wavelength of 1064 nm and the ejected electrons are found to have an energy of .137eV. The electron affinity is the difference in energy between the incident photons and the energy of the ejected electrons. Determine the electron affinity of thulium in units of electron volts per atom.

the electron affinity that I got was 1.003 eV/atom which was correct. However I am struggling the determine the electron affinity of thulium in units of kilojoules per mole. Thank you!

Re: Sapling Homework - electron affinity

Posted: Thu Oct 22, 2020 8:23 pm
by Carolina 3E
To convert 1.003eV/atom to kJ/mol, I used dimensional analysis
multiply (1.003eV/atom) by (6.022x10^23 atoms/mol) --> get eV/mol
then multiply by (1.602x10^-19 J/1 eV) --> get J/mol
then multiply by (1 kJ/1000 J) --> get kJ/mol

Re: Sapling Homework - electron affinity

Posted: Thu Oct 22, 2020 9:09 pm
by SamanthaTolentino 3D
I get 9.676 x 10^1 kj/mol however sapling still marks it incorrect. Is there another way to solve this problem?

Re: Sapling Homework - electron affinity

Posted: Sat Oct 24, 2020 5:35 pm
by Charlene D 3I
Yeah I couldn't get the right answer for the second part either. I wonder if there is anything wrong with my conversions.
@Samantha, could you explain your steps for the first part and how you got 1.003? I used E=hc/lambda and converted nm to m as well as J to eV, but I still didn't get to 1.003.
Thank you!

Re: Sapling Homework - electron affinity

Posted: Sun Oct 25, 2020 9:30 pm
by SashaAnand2J
Charlene D 3I wrote:Yeah I couldn't get the right answer for the second part either. I wonder if there is anything wrong with my conversions.
@Samantha, could you explain your steps for the first part and how you got 1.003? I used E=hc/lambda and converted nm to m as well as J to eV, but I still didn't get to 1.003.
Thank you!


Hi! I think the issue might be with the significant figures in your first answer! Although you stated 1.003 was the correct answer, with significant figures, I got an answer of 1.03, not 1.003 eV/atom for Part 1. Sapling might be at fault for this, since it probably accepts answers that are close enough. Double check your calculations to see what happened...it is possible you rounded before the last step! From 1.03 eV/atom, if you follow the dimensional analysis Samantha details, you should get the correct answer for Part 2.

Re: Sapling Homework - electron affinity

Posted: Mon Oct 26, 2020 5:32 pm
by magalysantos_1F
Charlene D 3I wrote:Yeah I couldn't get the right answer for the second part either. I wonder if there is anything wrong with my conversions.
@Samantha, could you explain your steps for the first part and how you got 1.003? I used E=hc/lambda and converted nm to m as well as J to eV, but I still didn't get to 1.003.
Thank you!

Make sure to double check your J to eV conversion! You divide the energy you got from E=hc/lambda by 1.602x10^-19 in order to get eV and subtract it by 0.137 eV in order to get 1.03 or 1.003 :)