## Question 1.25

$E=hv$

Kimberly 1H
Posts: 63
Joined: Fri Sep 28, 2018 12:17 am
Been upvoted: 1 time

### Question 1.25

1.25 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?

I calculated the energy in part A, emitted by a single sodium atom, by using E=h(c/$\lambda$) but I'm not sure how to set up parts B and C when larger quantities are involved.

Anusha 1H
Posts: 65
Joined: Fri Sep 28, 2018 12:15 am

### Re: Question 1.25

B and C are pretty similar to part A!

b) In order to determine the energy emitted, you need to know the number of atoms in the sample. Since we have a 5.00 mg mass we should first convert to grams. From there, use the molar mass to find the number of moles and then multiply that number by Avogadro's number to find the number of atoms.
Because the value you calculated in Part A is the amount of energy emitted in joules/atom, you can multiply this number by the number of atoms you calculated to find the energy emitted for the 5.00 mg sample

c)This is the same idea as part b. We need to find the number of atoms, and since we know there are 6.022 x 10^23 atoms/mol there are 6.022 x 10^23 atoms in this sample. Multiply this number again by the value you calculated in part A and you have the energy emitted (Joules/kJ).