Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ $mo{l}^{–1}$.

Answer 1

Energy of sodium (E)= $\frac{N_{A}hc}{\lambda }$
$\frac{(6.023\times {10}^{23}mo{l}^{-1})(6.626\times {10}^{-34}Js)(3\times {10}^{8}m{s}^{-1})}{242\times {10}^{-9}m}$
= $4.947\times {10}^{5}J$ $mo{l}^{–1}$
= $494.7\times {10}^{3}J$ $mo{l}^{–1}$
= 494 kJ $mo{l}^{–1}$