## Question 1.25b

$E=hv$

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### Question 1.25b

What is the specific equation for finding the energy of mass for this one problem why do we have to multiply the energy of the the sodium light with the moles and avogrado"s number?

Chem_Mod
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### Re: Question 1.25b

Could you post more information regarding this question? I cannot understand exactly what you need help because I do not understand the context.

Joshua Yang 1H
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Joined: Mon Jan 08, 2018 8:19 am

### Re: Question 1.25b

We're given that the wavelength of light emitted by the Na atoms = 589 x 10^-9 m

a) asks for the energy emitted by an excited sodium atom when it generates a photon
this deals with photons, which have no mass, therefore we use the equation E = hv and c = vλ

E = hv c = vλ so v = c/λ so E = hc/λ

now we plug in the values to get the answers :)

b) asks for the energy emitted by 5.00 mg of sodium atoms emitting light at this wavelength

For this we figure out the number of atoms we have in 5.00 mg = (5.00mg/molar mass of Na) x (avogadro's constant)
then multiply it by the amount of energy emitted per atom, which we got in part a)

c) asks for the energy emitted by 1.00 mol of Na

This is the same as idea as part b) but we already know the amount of mols of Na we have (1)