Answer
(a) $173.4\,kJ/mol$
(b) $8.6\,kJ/mol$
(c) $-2470.4\,kJ/mol$
Work Step by Step
Recall: $\Delta G^{\circ}=\Sigma n_{p}\Delta G_{f}^{\circ}(products)-\Sigma n_{r}\Delta G_{f}^{\circ}(reactants)$
(a) $\Delta G^{\circ}=[2\Delta G_{f}^{\circ}(NO,g)]-[\Delta G_{f}^{\circ}(N_{2},g)+\Delta G_{f}^{\circ}(O_{2},g)]$
$=[2(86.7\,kJ/mol)]-[(0\,kJ/mol)+(0\,kJ/mol)]$
$=173.4\,kJ/mol$
(b) $\Delta G^{\circ}=[\Delta G_{f}^{\circ}(H_{2}O,g)]-[\Delta G_{f}^{\circ}(H_{2}O,l)]$
$=(-228.6\,kJ/mol)-(-237.2\,kJ/mol)$
$=8.6\,kJ/mol$
(c) $\Delta G^{\circ}=[4\Delta G_{f}^{\circ}(CO_{2},g)+2\Delta G_{f}^{\circ}(H_{2}O,l)]-[2\Delta G_{f}^{\circ}(C_{2}H_{2},g)+5\Delta G_{f}^{\circ}(O_{2},g)]$
$=[4(-394.4\,kJ/mol)+2(-237.2\,kJ/mol)]-[2(209.2\,kJ/mol)+5(0)]$
$=-2470.4\,kJ/mol$
