Question

Fuel cells `:` Fuel cells are galvanic cells in which the chemical energy of fuel cell is directly converted into electrical energy. A type of fuel cell is a hydrogen `-` oxygen fuel cell. It consists of two electrodes made up of two porous graphite impregnated with a catalyst `(` platinum, silver, or metal oxide `).` The electrodes are placed in aqueous solution of `NaOH` . Oxygen and hydrogen are continuously fed into the cell. Hydrogen gets oxidized to `H^(o+)` which is neutralized by `overset(c-)(O)H, i.e.,` anodic reaction.

At cathode, `O_(2)` gets reduced to `overset(c-)(O)H`
Hence, the net reaction is
The overall reaction has
`DeltaH=-285.6 kJ mol^(-1)` and `DeltaG=-237.4 kJ mol^(-1)` at `25^(@)C`
What is the value of `DeltaS^(c-)` for the fuel cell at `25^(@)C`?
A. `-1600 JK^(-1)`
B. `-160 JK^(-1)`
C. `160 JK^(-1)`
D. `1600 JK^(-1)`

Answer 1

Correct Answer - B
`DeltaG^(@) = DeltaH^(@) - T DeltaS^(@)`
`DeltaH^(@) =- 285.6 kJ//mol`
`DeltaG^(@) =- 237.4 kJ//mol`
`- 237.4 =- 285.6 - 298 DeltaS^(@)`
`rArr -298 DeltaS^(@) =- 237.4 +285.6`
`rArr DeltaS^(@) =(-237.4 +285.6)/(298)`
`rArr DeltaS^(@) = (237.4 - 285.6)/(298)`
`=(-48.2)/(298) kJK^(-1) =- 1.61 xx 10^(2) JK^(-1) =- 161 JK^(-1)`