What is the energy in joules of one mole of photons associated with red light of
wavelength 7.00 x 102 nm?
A. 1.71 x 105
J B. 12.4 kJ
C. 4.72 x 10-43 J
D. 256 kJ
E. 2.12 x 1042 J
To calculate this energy per mole of photons we use the equation that relates the Planck's constant (h = 6.626 X 10-34 Js), the velocity of light (c = 2.998 X 108 m/s) , and wavelength [in meters] (λ = 7 X 10-7 m) as:
That was the energy per photon and we multiply it with Avogadro's constant (NA = 6.022 * 1023 mol-1) to have the energy per mole:
Substituting all the constants and wavelength give us as result:
In conclusion, option A (1.71 X 105 J) is the correct one.