How much energy (in j) is contained in 1.00 mole of 739 −nm photons?

The energy of a single photon of frequency f is equal to 

where h is the Planck constant. Using the relationship between frequency f and wavelength :

where c is the speed of light, we can rewrite the energy of the photon as

The photons in the problem have wavelength , so their energy is


However, this is the energy of a single photon. In the problem we have 1 mol of photon, and 1 mol corresponds to
photons (Avogadro number)
so, to find the total energy of 1 mol of photon, we should multiply the energy of a single photon by the number of photons: