Question

Silane, SiH4 burns in air. The products are solid SiO2 and gaseous water: $SiH_{4}(g)+2O_{2}(g) \longrightarrow SiO_{2}(s)+2H_{2}O(g)$
ΔG(kJ/mol):
-805
-228.6
52.3
0

Substance:
$SiO_{2}$
$H_{2}O$
$SiH_{4}$
$O_{2}$
Predict the spontaneity of the reaction.

Answer 1

"To predict whether the reaction is spontaneous or not, we should first calculate

${\Delta}_{r}{G}^{o}$

The reaction,

$Si{ H }_{ 4 }(g)\quad +\quad 2{ O }_{ 2 }(g)\quad \rightarrow \quad Si{ O }_{ 2 }(s)\quad +\quad 2{ H }_{ 2 }O\quad (g)$

${ \Delta}_{r}{ G }^{o}\quad =[{\Delta}_{f}{G}^{ o }({ SiO }_{ 2 })\quad +\quad 2{ \Delta}_{f}{ G }^{o}({ H }_{ 2 }O)\quad -\quad [{ \Delta}_{ f }{G}^{o}(Si{ H }_{ 4 })\quad +\quad 2{ \Delta}_{f}{G}^{ o }({ O}_{2})]$

${ \Delta}_{r}{G}^{o}\quad =\quad [-805\quad +\quad 2(-228.6)]\quad -\quad [+52.3\quad +\quad 2\quad \times \quad 0]$

${ \Delta}_{r}{ }^{o}\quad =\quad [-805\quad -\quad 457.2]\quad -\quad [52.3]$

${ \Delta}_{r}{G}^{o}\quad =\quad -1314.5\quad kJ/mol$"