2
Question
An electromagnetic radiation of wavelength 198 nm is sufficient to ionise a metal atom. Calculate the ionisation energy in kJmol−1,(Planck constant h=6.6×10−34 Js, Avogadro number=6.02×1023
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Solution
According to Planck's quantum theory,
The energy of radiation is inversely proportional to its wavelength which is given by, E=hcλ
Given,
λ=198×10−9 m
h=6.6×10−34 Js
As the electromagnetic radiation is just sufficient to ionize the sodium atom,
Ionization energy = Energy of the photon
∴E=hcλ
=6.6×10−34×3×108198×10−9
=10−18 J
=10×10−22 kJ/atom
Thus, for the ionisation of 1 atom, energy = 10×10−22 kJ is required.
∴ Energy required per mole = 10×10−22 kJ×6.02×1023
=602 kJmol−1
The energy of radiation is inversely proportional to its wavelength which is given by, E=hcλ
Given,
λ=198×10−9 m
h=6.6×10−34 Js
As the electromagnetic radiation is just sufficient to ionize the sodium atom,
Ionization energy = Energy of the photon
∴E=hcλ
=6.6×10−34×3×108198×10−9
=10−18 J
=10×10−22 kJ/atom
Thus, for the ionisation of 1 atom, energy = 10×10−22 kJ is required.
∴ Energy required per mole = 10×10−22 kJ×6.02×1023
=602 kJmol−1
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