Question #197098

What is the energy in joules of one mole of photons associated with red light of

wavelength 7.00 x 10^{2} 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 10^{42} J

Expert's answer

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 10^{8} 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 (N_{A} = 6.022 * 10^{23} 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 10**^{5}** J) is the correct one. **

Reference:

- Castellan, G. W. (1983). Physical Chemistry. Ed.

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