How do you do this chemistry problem?

Question

Calculate the energy difference (E) for the photon absorbed when a hydrogen atom undergoes a transition from n = 1 to n = 5 for 1 mol H atoms.

Answer 1

Without considering the fine structure, the electron energy level of the hydrogen atom can be written as:
En = -2.179×10^-18 J/ n^2
Thus for n = 5:
E5 = -8.716x10^-20 J
the energy difference (E) for the photon absorbed when a hydrogen atom undergoes a transition from n = 1 to n = 5:
E5 - E1 = 2.09x10^-18 J
For 1 mol H atoms:
6.022x10^23 *(E5 - E1) = 1.26x10^6 J = 1.26 MJ