Help!! Stuck on a Chemistry Question

[StillStanding]

:)

[AngieW in Texas]

In physics, we generally write the formula in terms of electronvolts, so the formula I would use is

E = (13.6eV)*(Z/n)^2

 

When I convert eV to J, I get 2.18*10^-18J, so the formula you are using looks correct.

 

hydrogen atom with n = 1

(2.18*10^-18J)(1/1) = 2.18*10^-18J

This is how many Joules it takes to remove an electron from the ground state in one hydrogen atom, but the answer is given in kJ/mol, so you're going to have to do a unit conversion.

(2.18*10^-18J/atom)(1kJ/1000J)(6.022*10^23atom/mol) = 1312kJ/mol

 

Then you need to do the same calculation with n=2

(2.18*10^-18J)(1/2)^2 = 0.545*10^-18J/atom

(0.545*10^-18J/atom)(1kJ/1000J)(6.022*10^23atom/mol) = 328kJ/mol

 

I don't get the answer you have for Li. When I do same the calculation for Li +2, I get 11815kj/mol.

Edited September 29, 2011 by AngieW in Texas

[regentrude]

Hello,

Please walk me through this problem so I can explain it to my dd. I have the answers but not the solutions and I can't figure out how they are calculating it to get the numbers they get, and why are the units from the first one different than the other two. I am feeling pretty dumb right now.:confused:

 

Chemistry Problem

Bohr's atomic theory can be used to calculate the energy required to remove an electron from an orbit of a hydrogen atom or an ion containing only one electron. This is the ionization energy. The formula for determining the ionization energy (E) is

 

E=Z (to the second power) x k / n (to the second power)

 

where Z is he atomic number, k is a 2.18 x 10*-18 J and n is the energy level.

 

What is the energy required to eject and electron from a hydrogen atom when the electron is in the ground state (n=1)? Answer: 1312 kJ/mol

 

for ONE H atom, use formula above with Z=1 and n=1.

To find energy per mole, multiply by Avogadro's number, 6.022 exp 23.

kJ means 10^3 J

You get above answer

 

In the second state? Answer=328 kJ

This should be per mole, too. It is 1/4 of the first energy, because n=2.

 

How much energy is required to eject a ground state electron from the species Li+? Answer=2.12 x 10*4 kJ

 

Should it not be a Li 2+, because the Bohr formula is for one-electron ions which resemble H? But the number does not work out... no idea how you get this one. (The order of magnitude suggests that this would be per mole as well)

[StillStanding]

Thank you, Thank you, Thank you...It has been over 20 years since I took my last chemistry class and the textbook we are using has not introduced moles or the Avogadro's number, 6.022 exp 23. yet (the problem was from the concept challenge section). Don't be surprised to hear from me again:001_smile: