Answer
$-432.8\,J\,mol^{-1}K^{-1}$
Work Step by Step
We find:
$\Delta S^{\circ}=\Sigma n_{p}S^{\circ}(products)-\Sigma n_{r}S^{\circ}(reactants)$
$=[S^{\circ}(SiO_{2},s)+2S^{\circ}(H_{2}O,l)]-[S^{\circ}(SiH_{4},g)+2S^{\circ}(O_{2},g)]$
$=[(41.84\,Jmol^{-1}K^{-1})+2(69.91\,Jmol^{-1}K^{-1})]-[(204.5\,Jmol^{-1}K^{-1})+2(205.0\,Jmol^{-1}K^{-1})]$
$=-432.8\,J\,mol^{-1}K^{-1}$
