Answer
(a) $47.5\,JK^{-1}mol^{-1}$
(b) $-12.5\,JK^{-1}mol^{-1}$
(c) $-242.8\,JK^{-1}mol^{-1}$
Work Step by Step
Recall: $\Delta S^{\circ}_{rxn}=\Sigma n_{p}S^{\circ}(products)-\Sigma n_{r}S^{\circ}(reactants)$
(a) $\Delta S^{\circ}_{rxn}=[S^{\circ}(Cu,s)+S^{\circ}(H_{2}O,g)]-[S^{\circ}(H_{2},g)+S^{\circ}(CuO,s)]$
$=[(33.3\,JK^{-1}mol^{-1})+(188.7\,JK^{-1}mol^{-1})]-[(131.0\,JK^{-1}mol^{-1})+(43.5\,JK^{-1}mol^{-1})]$
$=47.5\,JK^{-1}mol^{-1}$
(b) $\Delta S^{\circ}_{rxn}=[S^{\circ}(Al_{2}O_{3},s)+3S^{\circ}(Zn,s)]-[2S^{\circ}(Al,s)+3S^{\circ}(ZnO,s)]$
$=[(50.99\,JK^{-1}mol^{-1})+3(41.6\,JK^{-1}mol^{-1})]-[2(28.3\,JK^{-1}mol^{-1})+3(43.9\,JK^{-1}mol^{-1})]$
$=-12.5\,JK^{-1}mol^{-1}$
(c) $\Delta S^{\circ}_{rxn}=[S^{\circ}(CO_{2},g)+2S^{\circ}(H_{2}O,l)]-[S^{\circ}(CH_{4},g)+2S^{\circ}(O_{2},g)]$
$=[(213.6\,JK^{-1}mol^{-1})+2(69.9\,JK^{-1}mol^{-1})]-[(186.2\,JK^{-1}mol^{-1})+2(205.0\,JK^{-1}mol^{-1})]$
$=-242.8\,JK^{-1}mol^{-1}$
