Question

The ionization enthalpies of lithium and sodium are 520 kJ/mole and 495 kJ/mole respectively. The energies required to convert all the atoms present in 7 mg of lithium vapours and 23 mg of sodium vapours to their respective gaseous cations respectively are?

• A. 52 J, 49.5 J
• B. 520 J, 495 J
• C. 49.5 J, 52 J
• D. 495 J, 520 J

Answer 1

The correct option is B

520 J, 495 J

Number of moles of Li = $\frac{7\times {10}^{-3}}{7}$ = ${10}^{-3}$

Number of moles of Na = $\frac{23\times {10}^{-3}}{23}$ = ${10}^{-3}$

The amount of energy required for 1 mole of Li = 520 kJ.

For ${10}^{-3}$ of Li = 250 $\times$ ${10}^{-3}$ = 520 J

The amount of energy required for 1 mole of Na = 495 kJ.

For ${10}^{-3}$ of Na = 495 $\times$ ${10}^{-3}$ = 495 J