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NCERT Class XI Chemistry Structure of Atom Solutions

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Question : 10 of 67
Marks: +1, -0
Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ mol−1\mathrm{kJ\,mol}^{-1}.
Solution:  
Here, λ = 242 nm = 242 × 10−910^{-9} m
I.E. = hcλ\frac{hc}{\lambda} = 6.626×10−34×3×108242×10−9\frac{6.626 \times 10^{-34} \times 3 \times 10^8}{242 \times 10^{-9}} = 8.214 × 10−1910^{-19} J/atom
Ionisation energy of sodium in kJ mol−1\mathrm{kJ\,mol}^{-1} = 8.214 × 10−1910^{-19} × 10−310^{-3} × 6.022 × 102310^{23}
= 494.65 kJ mol−1\mathrm{kJ\,mol}^{-1}
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