Answer
(a) $11.62\,J/K\cdot mol$
(b) $174.69\,J/K\cdot mol$
Work Step by Step
Recall: $\Delta S^{\circ}_{rxn}=\Sigma nS^{\circ}(products)-\Sigma mS^{\circ}(reactants)$
(a) $\Delta S^{\circ}_{rxn}=[S^{\circ}(SO_{2})]-[S^{\circ}(S)+S^{\circ}(O_{2})]$
$=[(248.5\,J/K\cdot mol)]-[(31.88\,J/K\cdot mol)+(205.0\,J/K\cdot mol)]=11.62\,J/K\cdot mol$
(b) $\Delta S^{\circ}_{rxn}=[S^{\circ}(MgO)+S^{\circ}(CO_{2})]-[S^{\circ}(MgCO_{3})]$
$=[(26.78\,J/K\cdot mol)+(213.6\,J/K\cdot mol)]-(65.69\,J/K\cdot mol)$
$=174.69\,J/K\cdot mol$
