One end of a rope is tied to a 40 kg weight while the second end is coupled with an electric generator. A labourer lifts the weight up to 3 metre and then allows it to fall. As a result, the electric generator generates equal amount of electric work. The standard free energy change for the reaction ${\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{Na}\left(\mathrm{s}\right)\to 3{\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)+2\mathrm{Al}\left(\mathrm{s}\right)$is 451 kJ/mol of ${\mathrm{Al}}_2{\mathrm{O}}_3$ . The number of times the weight is lifted and dropped to produce 13.5 g aluminum will be if $\mathrm{g}=9.8 \mathrm{m}/{\mathrm{s}}^2$.