Question

Silane `(SiH_(4))` burns in air as:
`SiH_(4)(g) +2O_(2)(g) rarr SiO_(2)(s) +2H_(2)O(l)`
the standard Gibbs energies of formation of `SiH_(4)(g), SiO_(2)(s)`, and `H_(2)O(l)` are `+52.3, -805.0`, and `-228.6kJ mol^(-1)`, respectively. Calculate Gibbs enegry change for the reaction and predict whether the reaction in spontaneous or not.

Answer 1

`SiH_(4)(g) +2O_(2)(g) rarr SiO_(2)(g) +2H_(2)(g)`
`Delta_(r)G^(Theta) = Delta_(r)G^(Theta) (SiO_(2)) +2Delta_(f)G^(Theta) (H_(2)O)`
`-[Delta_(f)G^(Theta) (SiH_(4))+2Delta_(f)G^(Theta)(O_(2))]`
`=- 805.0 +2(-228.6) -[+52.3 +2(0)]`
`= - 805.0 -457.2 - 52.3`
`=- 1314.5 kJ`
Since `Delta_(r)G^(Theta)` is negative, the reaction will be spontaneous.