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Fuel cells : Fuel cells are galvanic cel...

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`
If the cell voltage is `1.23V` for the `H_(2)-O_(2)` fuel cell and for the half cell `:`

A

`0.41V`

B

`0.83V`

C

`-0.41V`

D

`-0.83V`

Text Solution

Verified by Experts

The correct Answer is:
D

The cell reaction is
`{:(2H_(2)+O_(2) hArr 2H_(2)O, E^(@) = 1.23 V, eq(i)),("For" O_(2)+3H_(2)O +4e^(-)hArr 4OH^(-),E^(@) =0.40V,eq.(ii)):}`
Hence for the reaction
`2H_(2)O +e^(-) hArr H_(2)+2OH^(-)` or `4H_(2)O +e^(-) hArr 2H_(2) +4OH^(-)` eq.(iii)
eq.(i)-eq(ii) gives the equation
`2H_(2)+4OH^(-) hArr 4H_(2)O +4e^(-)`
Hence for the equation
`4H_(2)O +4e^(-) hArr 2H_(2)+4OH^(-) E^(@) =- 0.83 V`
or for `2H_(2)O +2e^(-) hArr H_(2)+2OH^(-)`also `E^(@)` is `-0.83 V`
Hence choice (D) is correct and all others are incorrect.
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Knowledge Check

  • 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 J K^(-1)`
    B
    `-160 J K^(-1)`
    C
    `160 J K^(-1)`
    D
    `1600 J K^(-1)`
  • A fuel cell is

    A
    the voltaic cells in which discontinuous supply of fuels are send at anode to give oxidation
    B
    the voltaic cell in which fuels such as : `CH_(4) , H_(2) , CO` are used up at anode
    C
    it involves the reactions of `H_(2) - O_(2)` fuel cell such as
    Cathode : `2 H_(2) + 4OH^(-) to 4 H_(2) O(l) + 4e`
    Anode : `O_(2) + 2 H_(2)O (l) + 4e to 4 OH^(-)`
    D
    the efficiency of a `H_(2) - O_(2)` fuel cell is very low
  • 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 Suppose the concentration of hydroxide ioin in the cell is doubled, then the cell voltage will be

    A
    Reduced by half
    B
    Increased by a factor of 2
    C
    Increased by a factor of 4
    D
    Unchanged
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    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 A fuel cell is I. A voltaic cell in which continuous supply of fuels are sent at anode to perform oxidation. II. A voltaci cell in which fuels such as :CH_(4),H_(2), and CO are used up at anode. III. One which involves the reaction of H_(2)-O_(2) fuel cell such as : Anode :2H_(2)O+4overset(c-)(O)H rarr 4H_(2)O(l)+4e^(c-) Cathode : O_(2)+2H_(2)O(l) =4e^(-) rarr 4overset(c-)(O)H IV. The efficiency of H_(2)-O_(20 fuel cell is 70 to 75%

    Purpose of hydrogen -oxygen fuel cell is to

    The overall reactions of a hydrogen -oxygen fuel cell is

    When a fuel cell is discharged

    The device which converts chemical energy of fuels directly into electrical energy is