Question

Standard free energies of formation in kJ/mol) at 298 K are -237.2, -394.4 and -8.2 for `H_(2)O(l),CO_(2)(g)` and pentane (g) respectively. The value of `E_(cell)^(@)` for the pentane-oxygen fuel cell is
A. 1.968 V
B. 2.0968V
C. 1.0968V
D. 0.0968V

Answer 1

Correct Answer - C
The balanced equation for pentane-oxygen cell reaction will be
`C_(5)H_(12)+8O_(2)to5CO_(2)+6H_(2)O,n=32`
`Delta_(r)G^(@)=[5xxDelta_(f)G^(@)(CO_(2))+6Delta_(f)G^(@)(H_(2)O)]-[Delta_(f)G^(@)(C_(5)H_(12))+8Delta_(f)G^(@)(O_(2))]`
`=[5(-394.5)+6(-237.2)]-[(-8.2)+0]`
`=-1972-1423.2+8.2=-3387" kJ "mol^(-1)`
`Delta_(f)G^(@)=-nFE_(ceLL)^(@)`
`therefore-3387000=-32xx96500xxE_(cell)^(@)`
or `E_(cell)^(@)=1.0968V`