Answer
$-364\,kJ/mol$
Work Step by Step
We find:
$\Delta G^{\circ}_{rxn}=\Delta H^{\circ}_{rxn}-T\Delta S^{\circ}_{rxn}$
$\Delta H^{\circ}_{rxn}=\Sigma n\Delta H_{f}^{\circ}(products)-\Sigma n\Delta H_{f}^{\circ}(reactants)$
$=[4(-1281\,kJ/mol)]-[(-2984\,kJ/mol)+6(-285.8\,kJ/mol)]$
$=-425.2\,kJ/mol$
$T=298\,K$
$\Delta S^{\circ}_{rxn}=\Sigma nS^{\circ}(products)-\Sigma nS^{\circ}(reactants)$
$=[4(110.5\,J/mol\cdot K)]-[(228.9\,J/mol\cdot K)+6(69.91\,J/mol\cdot K)]$
$=-206.36\,J\,mol^{-1}K^{-1}$
Then,
$\Delta G^{\circ}_{rxn}=(-425200\,J/mol)-(298\,K)(-206.36\,J\,mol^{-1}K^{-1})$
$=-364000\,J/mol=-364\,kJ/mol$
