Question

Determine the energy of 1.80 mol of photons for each of the following kinds of light. (Assume three significant figures.) visible light (520 nm ). ultraviolet radiation (145 nm ). Express your answer using three significant figures.

Answer 1

use the formula

Energy = hc/lambda

where h=planks constant = 6.626 x10^-34 js
c= speed of light = 3x10^8 m/s
lambda= wave length of visible light = 520 nm = 520 x10^-9 m

E = 6.626 x10^-34 js*3x10^8 m/s/520 x10^-9 m
= 3.82 x10^-19 J

This energy is for 1 photon

now calculate energy for 1 mol ; for that multiply energy by avogadro number [6.022 x10^23 ]

since 1 mole photon contain avogadro number of particles ,then multiply by 1.80 will give energy for 1.8 mol photon.

Energy =3.82 x10^-19 J * 6.022 x10^23* 1.8 mol =41.40 x10^4 j.mol

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for UV, lambda = 145 nm = 145 x10^-9 nm

E=hc/lambda
=6.626 x10^-34 js*3x10^8 m/s/145 x10^-9 m
= 13.7x10^-19 J

energy for 1.80 mol photon =13.7x10^-19 J*6.022 x10^23 ]*1.8 mol =148.5 x 10^4 j.mol
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:)