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Question:

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionize the sodium atom. Calculate the ionization energy of sodium in kJ/mol.

Solution:

The ionization energy of sodium will be equal to the energy possessed by the radiation of wavelength 242 nm. It is E=hc/λ=6.626×10⁻³⁴Js×3×10⁸/242×10⁻⁹m=8.21×10⁻¹⁹J. The ionization energy per mole is 8.21×10⁻¹⁹×6.023×10²³=494000J=494kJ.