Question

The Ionisation energy of Li is 520 kJ $mo{l}^{–1}$. The amount of energy required to convert 140 mg of Li atoms into gaseous $L{i}^{+}$ ions is:

• A. 10.4 kJ
• B. 520 kJ
• C. 72.8 kJ
• D. 3.71 kJ

Answer 1

The correct option is A

10.4 kJ

Number of moles of $Li=\frac{\text{Mass}}{\text{atomic mass}}$

= $\frac{140\times {10}^{-3}}{7}=2\times {10}^{-2}$ mol

For the conversion of 1 mole atoms of Li into $L{i}^{+}$, the energy required is 520 kJ/mol

$\therefore$ For the conversion of $2\times {10}^{-2}$ mole atoms of Li into $L{i}^{+}$ ions, the energy required will be $520\times 2\times {10}^{-2}=10.4kJ$