Consider the following chemical changes,
$\begin{array}{l}\mathrm{I}:{\mathrm{CaC}}_2\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(1\right)⟶\mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{s})+{\mathrm{C}}_2{\mathrm{H}}_2(\mathrm{g})\\ \mathrm{II}:2{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{SO}}_3\left(\mathrm{g}\right)\\ \mathrm{III}:2\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)⟶{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\end{array}$
Work is done by the system in the cases of