## Chemistry: The Central Science (13th Edition)

The energy of $1mol$ of 320-nm photons is $$E\approx3.737\times10^5J$$
First, we need to calculate the energy of a photon according to the formula $$E_p=h\nu$$ $h$: Planck's constant $(h\approx6.626\times10^{-34}J.s)$ 1) We know from part a) that the frequency of the light related to the mentioned photons is $\nu\approx9.369\times10^{14}s^{-1}$ Therefore, the energy of a 320-nm photon is $$E_p=h\nu$$$$E_p=(6.626\times10^{-34}J.s)\times(9.369\times10^{14}s^{-1})$$$$E_p\approx6.208\times10^{-19}J$$ 2) $1mol$ of photons equals $6.02\times10^{23}photons$ So, the energy of $1mol$ of 320-nm photons is $$E=(6.02\times10^{23}photons)\times(6.208\times10^{-19}J/photon)$$$$E\approx3.737\times10^5J$$