On the basic of the following `Delta_(r)G^(Theta)` values at `1073K`:
`S_(1)(s) +2O_(2)(g) rarr 2SO_(2)(g) Delta_(r)G^(Theta) =- 544 kJ mol^(-1)`
`2Zn(s) +O_(2)(g) rarr 2ZnO(s) Delta_(r)G^(Theta) =- 480 kJ mol^(-1)`
`2Zn(s) +S_(2)(s) rarr 2ZnS(s) Delta_(r)G^(Theta) =- 293 KJ mol^(-1)`
Show that roasting of zinc sulphide to zinc oxide is a spontaneous process.

Options

A. `-357 KJ`
B. `-731 KJ`
C. `-773 KJ`
D. `-229 KJ`

Answer

B

Explanation

`DeltaG` of formation of different substance are as
`2SO_(2) =-544 KJ`
`2 ZnS=-293 KJ`
`2ZnO=-480 KJ`
For the reaction,
`2ZnS+ 3O_(2)(g) to 2ZnO(s) + 2SO_(2)(g)`
`DeltaG=[(DeltaG_("(products)")-DeltaG_("(reactants)")]`
`[(-480) + (-544)-(-293)]`
`=-1024 + 293 =- 731 KJ`