A light emitting diode (L.E.D.) emits photons with an energy of #2.84 xx 10^-19# J. What is the energy per mole of photons emitted?
The molar energy of the photons is 171 kJ/mol.
Just as a dozen is twelve of anything, so a mole is Avogadro's number =
This is similar in magnitude to the energy involved in chemical reactions, accounting for the fact that light often drives chemical reactions. One real-world example of this is given in https://en.wikipedia.org/wiki/Photosynthesis.