## Photoelectric Effect Module #28B

Emma Strassner 1J
Posts: 62
Joined: Wed Sep 30, 2020 9:50 pm

### Photoelectric Effect Module #28B

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. How much energy is required to remove an electron from one sodium atom?

Hi, I know this is the problem where the value for the work function comes into play. However, I am confused as to how we use it to find the energy needed to remove the electron?

Jordan Tatang 3L
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### Re: Photoelectric Effect Module #28B

Hi! So the work function actually tells you how much energy is required to remove one electron from a metal. So in this question they give you the work function except it is in kJ per mol. The units of the work function that you want is in J per photon. Therefore for this question you just want to convert the given work function into the correct units. First you would multiply my 1000 to convert from kJ to J and then you would divide by Avogadro's constant in order to find out the energy per photon rather than a mol of photons.

Danielle DIS2L
Posts: 61
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Photoelectric Effect Module #28B

Hi!

So first, I multiplied 150.6kJ mol by 1000 to convert it to Joules which would equal to 156000J. We divide by Avogrado's constant because the question is asking how much energy is required to remove an electron from ONE sodium atom.

Emma Strassner 1J
Posts: 62
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Photoelectric Effect Module #28B

Hi! I was missing the division by Avogadro's number, so that makes much more sense! Thank you!

MCalcagnie_ 1D
Posts: 55
Joined: Wed Sep 30, 2020 10:08 pm

### Re: Photoelectric Effect Module #28B

Hi, I'm confused why you would use Avogadro's number here and not Planck's constant? Aren't we using E = hv, so wouldn't you just use Planck's constant? Does it matter that it is one mole, I didn't know that influenced this.

Jordan Tatang 3L
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Joined: Wed Sep 30, 2020 9:31 pm
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### Re: Photoelectric Effect Module #28B

MCalcagnie_ 2H wrote:Hi, I'm confused why you would use Avogadro's number here and not Planck's constant? Aren't we using E = hv, so wouldn't you just use Planck's constant? Does it matter that it is one mole, I didn't know that influenced this.

So the question asks for the energy required to remove one electron from one sodium atom. In the photoelectric effect, we can see that one photon is used to remove one electron. The energy required to remove that one electron is the work function which is already given to us in the question but it is in the units kJ/mol. Therefore you want to find the J per photon in order to find out how much energy is required per photon.

E = hv isn't necessary in this question because the work function is already given. If they provided the frequency of the light or the wavelength, then you would use that equation.

Hopefully that clears some things up!

MCalcagnie_ 1D
Posts: 55
Joined: Wed Sep 30, 2020 10:08 pm

### Re: Photoelectric Effect Module #28B

Ohhh okay! That makes more sense! Thank you!