[sn1sn2e1e2]

What is the energy of photons with a wavelength of 434 nm?

(A) 2.76 e5 kJ/MOL
(B) 2.76 e2 kJ/mol
(C) 2.76 e-1 kJ/mol
(D) 2.76 e-4 kJ/mol

Ok, I used the simple equation E=hv and changed it to E=(hc)/λ and using right units(nm to m and J to kJ) got 4.58e-22 kJ/mol. This does not match any from above! Then I realized that the choices were in units per mol so multiplied by 6.022e23 which gives you B(right).

However, how do you know you are supposed to multiply by Avogadro's constant when you do not know the "units" (other than Joules)?? Can't you divide your answer by 6.022 e23 to turn the answer to per moles?

[Borek]

It follos from tjhe definition of mole. What you calculated was energy of a single photon, and mole is N_A of whatever (I like to call it an overgrown dozen).

[sn1sn2e1e2]

It follos from tjhe definition of mole. What you calculated was energy of a single photon, and mole is N_A of whatever (I like to call it an overgrown dozen).

So it's like:

[4.58e-2 kJ / (single "photon")] times (6.022e23 "individual photons")/mol photon

photon cross out

Thanks Borek!