Answer:
E = 1.8 x 10⁵ J/mol
Explanation:
We are being asked the enery per mol for an emission line corresponding to 649 nm.
The energy of a photon is given by the porduct of Planck's contant times the frequency of the radiation,
E = hν
We also know that the frequency is given by
ν = c/λ
where c is the speed of light (3 x 10 ^8 m/s) and λ is 649 nm given in the problem. Therefore the energy per photon will be given by
E= hc/λ = 6.626 x 10⁻³⁴Js x 3 x 10 ^8 m/s/ 649 x 10 ⁻⁹ m
E = 3.1 x 10 ⁻¹⁹ J/ photon
(Note the wavelength has to be in nanometers (1nm= 10⁻⁹ m) and that the energy we get is the energy per a single photon. Thus we will need to multiply this result by Avogadro's number to answer this question.
E = 3.1 x 10 ⁻¹⁹ J/ photon x 6.022 x 10 ²³photon/mol
E = 1.8 x 10⁵ J/mol
