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### Chapter 1 Question 25

Posted: Tue Oct 17, 2017 1:24 am
Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. 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 for question 25, I got the answer for part A, but in part B it gives 5.00 mg of sodium atoms. Would you find the number of atoms in 5.00 mg and then multiply it by your answer in part A to find the Joules of energy emitted?

### Re: Chapter 1 Question 25  [ENDORSED]

Posted: Tue Oct 17, 2017 1:43 am
For part B you would need to convert the 5.00 mg of sodium atoms into mols of sodium, convert that mol value into the number of atoms (using Avogradro's number), and then multiply the number of atoms by the energy (J) value you found in part A.

For part C you basically do the same thing except you know that you have 1.00 mol of sodium.

### Re: Chapter 1 Question 25

Posted: Wed Oct 18, 2017 1:48 pm
Think about it as if you are finding the energy of one photon in part a, and then in part b you are finding the energy of multiple photons. So since you found the energy of one photon in the first part, all you would have to do is convert 5.00 mg of sodium into number of photons, and then multiply it by the energy that you calculated in part a!

### Re: Chapter 1 Question 25

Posted: Tue Apr 24, 2018 10:43 pm
So for part c since we already know the 1.00 mol of Na would we just multiply by Avogadro's number and by the E we found in a? or just by Avogadro's number?

### Re: Chapter 1 Question 25

Posted: Wed Apr 25, 2018 2:15 am
Yes, that is correct. You would take the E from part a (3.37 x 10^-19) multiply by Avogadro's number (6.022 x 10^23)