homework weeks 2,3,4 #12

[Kaylee Nezwek 1D]

Hi! This question is asking to find the electron affinity in eV/atom and kJ/mol, and I'm having trouble with the conversions. First, I used E=hc/wavelength to find the energy of the incident protons, which I found to be 1.867*10^-19 J. I converted this to eV by dividing by 1.602*10^19 J, getting 1.165 eV. 1.165 eV - 0.137 eV is 1.028. I tried multiplying this by Avogadro's constant, getting 7.02*10^23, but its telling me this answer is wrong for eV/atom. Also, for kg/mol, I multiplied 1.867*10^-19 J by 10^-3 to get kJ (I got 1.867*10^-22 kJ), and then also multiplied 0.137 eV by 1.602*10^19 J, and then 10^-3 to get 2.19*10^-23 kJ. I then multiplied the difference between these numbers by Avogadro's constant, but this was also wrong. Does anyone know what Im doing wrong?

[Anh Trinh 1J]

Once you subtract 1.165 eV - 0.137 eV, you do not need to multiply by the Avogadro’s constant because the units are already in eV/atom.

To find the kg/mol, convert 1.028 eV/atom to eV/mol by multiplying 1.028 with Avogadro’s constant. We then get 6.195x10^23 eV/mol. Now convert this to kJ/mol. The conversion from eV to Joule is 1 eV= 1.602 x10^-19 J. Then divide it by 1000 since 1 kJ = 1000 J. The answer I got in the end is 99.21 kJ/mol.

[BrittneyMyint1D]

Hi, so for the first part, you don't have to multiply 1.028 by Avogadro's constant, so the answer is just 1.028 eV/atom.
For the second part, the conversion from eV to J is 1.602*10^-19 J, so you may have forgotten the negative sign. I would recommend just using the answer you got from the first part and converting the units from eV/atom to kJ/mol. Just multiply 1.028 eV/atom by 1.602*10^-19 J to go from eV to J, by Avogadro's constant to go from atoms to mol, and divide by 1000 to go from J to kJ.

Hope this makes sense!

[Blake Ballew 1H]

Hello,

Once you get 1.028 you then simply multiply it by 1.602 x 10^-19 and by Avogadro's constant and then divide it by 1000. This should give you an answer of 99.21 kJ per mole. It seem you added a few unnecessary steps.

Hope this helps!

[Ralph Zhang 2L]

As previously mentioned, you do not need to re-convert the eV by multiplying it by Avogadro's number. Once you find the answer to the first one, you can just convert that answer to kg then multiply that by Avogadro's number. No need to redo any extra work.