Question

A 8.00 mL ampule of a 0.100 M solution of naphthalene in hexane is excited with a flash of light. The naphthalene emits 18.5 J of energy at an average wavelength of 349 nm. What percentage of the naphthalene molecules emitted a photon?

Answer 1

E = hc/λ    

   = (6.625 x 10^-34) x (3 x 10^8) / (349 x 10^-9)

   =5.69 x 10^-19 J

number of photons emitted = 18.5 / 5.69 x 10^-19

                                              = 3.25 x 10^19

moles of napthalene = 8 x 0.1 / 1000 = 8 x 10^-4

number of molecules = 8 x 10^-4 x (6.023 x 10^23) = 4.82 x 10^20

% = 3.25 x 10^19   x 100 / 4.82 x 10^20

       = 6.74 %

percentage of the naphthalene molecules emitted a photon = 6.74 %