## 1B.7

Duby3L
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

### 1B.7

Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589nm. How much energy is emitted by:
a) an excited sodium atom when it generates a photon
b) 5.00 mg of sodium atoms emitting light at this wavelength
c) 1.00 mol of sodium atoms emitting light at this wavelength

So part b I calculated the atoms of Na, but I don't know where to go from there.

Jane Burgan 1C
Posts: 73
Joined: Fri Sep 28, 2018 12:15 am

### Re: 1B.7

You would first find the number of moles of sodium atoms that 5.00 mg contains by dividing 5.00 mg by sodium's molar mass, then multiply that value by avogardo's number because that would transform the number of moles to the number of atoms that 5.00 mg of NA is. Finally, multiply that value by the energy value of one sodium atom that you got in part a:
(5.00 x 10^-3 g Na/22.9 g mol-1) * (6.022 x 10^23 atoms/mol) * (3.37 x 10^-19 J/atoms) = 44.1 J

Duby3L
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

### Re: 1B.7

Where did you get the energy of sodium from?

Diana Bibireata 1B
Posts: 60
Joined: Fri Sep 28, 2018 12:23 am

### Re: 1B.7

For part a you use the equation $E=ch/\lambda$
(because c and h are constants and the problem gives you the wavelength). This gives you the energy of a sodium atom. Then, for part b, after you find the number of atoms of sodium, you simply multiply it by the energy of one sodium atom.

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