In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is `:`
`CH_(3)OH_((l))+(3)/(2)O_(2(g))rarr CO_2((g))+2H_(2)O_((l))`
At `298K` standard Gibb's energies of formation for `CH_(3)OH(l), H_(2)O(l)` and `CO_(2)(g)` are `-166.2,-237.2` and `-394.4kJ mol^(-1)` respectively. If standard enthalpy of combustion of methanol is `-726kJ mol^(-1)`, efficiency of the fuel cell will be `:`

Options

A. `90%`
B. `97%`
C. `80%`
D. `87%`

Answer

B

Explanation

Efficienty `=(Delta G^(@))/(Delta H^(@))xx100`
`CH_(3)OH_((l))+(3)/(2)O_(2(g))rarr CO_(2(g))+2H_(2)O_((l))`
`Delta G^(@)=-702.6 kJ mol^(-1)`
`therefore` efficiency `=(-702.6)/(726)xx100=97%`