## HW 1.25 (b)

$E=hv$

Chau Nghiem 1K
Posts: 3
Joined: Fri Sep 25, 2015 3:00 am

### HW 1.25 (b)

Question: Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by 5.00 mg of sodium atoms emitting light at this wavelength?

Could someone explain why it's possible that the units for energy is able to conveniently switch from just J to J/atoms in order to cancel out the necessary units in part (b)? Thank you.

ConnieDo3I
Posts: 31
Joined: Fri Sep 25, 2015 3:00 am

### Re: HW 1.25 (b)

Hey!
So according to the solutions manual,
E = (5.00 x 10^-3 g Na / 22.99 g x mol^(-1)) x (6.022x10^23 atoms x mol^(-1)) x (3.37x10^(-19) J x atom^(-1)) = 44.1 J

If you follow the equation, the "atoms" unit should cancel out smoothly.
The following is the equation with only the units. It's probably easier to see how they cancel out this way.

g 1 atoms J
-- x ----------- x -------- x ------ = J
1 g mol^-1 mol atom

Hope this helps!

Angelica Dis 3k
Posts: 6
Joined: Fri Jun 23, 2017 11:40 am