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Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom .Calculate the ionisation energy of sodium in Kj `mol^(-1)`

Text Solution

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where `lambda = 242 nm = 242 xx 10^(9) m` wavelength per photon `E= (hc )/(lambda ) ` per mole E = `(N_(A) hc )/( lambda )`
`n= 6.626 xx 10^(34) Js`
`c=3.0 xx 10^(8) m`
`N_(A) = 6.022 xx 10^(23)` per mole
`=(6.022 xx 10^(23) mol^(1) xx 6.626 xx 10^(34) js xx 3.0 xx 10^(8) ms^(-1)J)/( (242 xx 10^(9) m))`
`=494.7 xx kJ mol^(-1) 495 kJ mol^(1)`
Ionisation enthalpy =495 kJ `mol^(1)`
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