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Fuel cell - class-XI

Description: fuel cell
Number of Questions: 20
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Tags: electrochemistry and chemical kinetics chemistry energy electrochemistry
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The overall reaction of a hydrogen-oxygen fuel cell is:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$

  2. $2H _{2(g)}+4OH^- _{(aq)}\rightarrow 4H _2O _{(l)}+4e^-$

  3. $O _{2(g)}+2H _2O _{(l)}+4e^-\rightarrow 4OH^- _{(aq)}$

  4. $4OH^- _{(aq)}+4e^-\rightarrow 2H _2O _{(l)}$

Show answer
Correct Option: A
Explanation:
A fuel cell is an electrochemical cell that converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen fuelwith oxygen or anotheroxidizing agent.
The reactions which takes place in hydrogen-oxygen fuel cell are,
At cathode:$2H _{2(g)}+4OH^{-} _{(aq)}\rightarrow 4H _2O _{(l)}+4e^{-}$
At cathode:$O _{2(g)}+2H _2O _{(l)}+4e^{-}\rightarrow 4OH^{-} _{(aq)}$
Overall reaction: $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$

$H _{2}-O _{2}$ fuel cell is:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. primary cell

  2. secondary cell

  3. both

  4. cant be predicted

Show answer
Correct Option: B
Explanation:

The hydrogen-oxygen fuel cell is the secondary voltaic cell. When the direction of current is reversed, the original reactants can be regenerated and the cell can be recharged.

Hydrogen -Oxygen fuel cells are used in space craft to supply:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. power for heat and light

  2. electrical power

  3. oxygen

  4. water

Show answer
Correct Option: B
Explanation:

In spacecrafts, the hydrogen oxygen fuel cell is a source of electrical power. 

Hence, option $B$ is correct.

In which reactants are not contained within the cell but are continuously supplied from external source?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. Fuel cell

  2. Dry cell

  3. Lithium battery

  4. Lead storage battery

Show answer
Correct Option: A
Explanation:

In fuel cell ( such as hydrogen oxygen fuel cell), the reactants are continuously supplied from external source.

Hence, option A is correct.

Which one of the following cells can convert chemical energy of $O _{2}$ and $H _{2}$ directly into electrical energy:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. mercury cell

  2. danicell cell

  3. fuel cell

  4. lead storage cell

Show answer
Correct Option: C
Explanation:

In hydrogen- oxygen fuel cell, the hydrogen is fuel and oxygen is the oxidizing agent. In this cell, the energy of combustion of hydrogen is converted into electrical energy.
Hence, option C is correct.

Which of the following statements is true for fuel cells ?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. They are more efficient

  2. They are free from pollution

  3. They run till reactants are active

  4. All of the above

Show answer
Correct Option: D
Explanation:

The fuel cells are more efficient. The energy efficiency of fuel cells is around 70 %. The only reaction product is water. Hence the fuel cells are free from pollution. The reactants are continuously supplied from external source. Hence fuel cells run till reactants are active.

In fuel cell oxidants used are:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $O _{2}$

  2. $H _{2}O _{2}$

  3. $HNO _{3}$

  4. All

Show answer
Correct Option: D

The efficiency of a fuel cell is given by:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $\frac{\Delta S}{\Delta G}$

  2. $\frac{\Delta H}{\Delta G}$

  3. $\frac{\Delta G}{\Delta S}$

  4. $\frac{\Delta G}{\Delta H}$

Show answer
Correct Option: D
Explanation:
The fuel cell thermodynamic efficiency is given by the ratio of the Gibbs function change to the Enthalpy change in the overall cell reaction. The Gibbs function change measures the electrical work and the enthalpy change is a measure of the heating value of the fuel. 
Efficiency = $ \frac{dG}{dH} $$=\frac{\Delta G}{\Delta H}$

If a fuel cell methanol is used as fuel and oxygen gas is used as an oxidiser. The reaction is $CH _3OH _{(l)} +\frac{3}{2}O _{2(g)} \rightarrow CO _{2(g)}+2H _2O _{(g)}$ at 298 K standard Gibb's energies of formation for $CH _3OH(l)H _2O(l)$ and $CO _2(g)$ are $-166.2$, $-237.2$ and $394.4$ $KJ \ mol^{-1}$ respectively. If standard enthalpy of combustion of methanol is -726 KJ $mol^{-1}$, efficieny of the fuel cell will be 

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. 80%

  2. 87%

  3. 90%

  4. 97%

Show answer
Correct Option: A

What is the approximate value of $ \Delta S^{\circ} $ for the fuel cell reaction at $ 25^{\circ}$? 

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $ -0.1624\,JK^{-1}$

  2. $ -162.4\,JK^{-1} $

  3. $ +162.4\,JK^{-1} $

  4. $ +0.1624\,JK^{-1} $

Show answer
Correct Option: B

Which of the following is an example of simple fuel cell?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. Lead storage battery

  2. Leclanche cell

  3. $H _2 O _2$

  4. All of the above

Show answer
Correct Option: C
Explanation:

A fuel cell makes electricity using the energy released by mixing fuel with air, a reaction which creates water and sometimes also carbon dioxide. The most common fuel for fuel cells is hydrogen, which when reacted with oxygen from air produces only water.
$H _{ 2 }O _{2}$ is simple fuel cell which generates electricity by reduction of $H _{ 2 }$ & $O _{ 2 }$.   

Identify the reaction taking place at cathode in fuel cell.

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$

  2. $2{H} _{2}+4{OH}^{-}\rightarrow 4{H} _{2}O+4{e}^{-}$

  3. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}+{H}^{+}$

  4. $4{H} _{2}O+4{e}^{-}\rightarrow 2{H}^{2}+4{OH}^{-}$

Show answer
Correct Option: A
Explanation:

In a fuel cell the hydrogen enters the fuel cell at the anode. A chemical reaction strips the hydrogen molecules of their electrons and the atoms become ionized to form $H^+$. The electrons travel through wires to provide a current to do work. The oxygen enters at the cathode, usually from the air. The oxygen picks up the electrons that have completed their circuit. The oxygen then combines with the ionized hydrogen atoms $(H^+)$, and water $(H _2O)$ is formed as the waste product which exits the fuel cell. 
Cathode side (a reduction reaction): $O _2 + 4H^+ + 4e^- \rightarrow 2H _2O$
or ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$

Which of the following reactions is used to make a fuel cell?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $Cd(s) + 2Ni(OH) _{3} (s) \rightarrow CdO(s) + 2Ni(OH) _{2} (s) + H _{2}O(l)$

  2. $Pb(s) + PbO _{2}(s) + 2H _{2} SO _{4}(aq) \rightarrow 2PbSO _{4}(s) + 2H _{2}O(l)$

  3. $2H _{2}(g) + O _{2}(g) \rightarrow 2H _{2}O(l)$

  4. $2Fe(s) + O _{2}(g) + 4H^{+} (aq) \rightarrow 2Fe^{2+}(aq) + 2H _{2}O(l)$

Show answer
Correct Option: C
Explanation:

Reaction used in fuel cell is
$2H _{2}(g) + O _{2}(g) \rightarrow 2H _{2}O (l)$

At anode: $[H _{2} \rightarrow 2H^{+} + 2e]\times 2$
At cathode: $O _{2} + 2H _{2}O + 4e\rightarrow 4OH^{-}$

Hence, option C is correct.

An examples of a simple fuel cell is:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. lead storage battery

  2. $H _{2} - O _{2}$ cell

  3. daniell cell

  4. lechlanche cell

Show answer
Correct Option: B
Explanation:
$\rightarrow$ The galvanic cells in which the energy of combustion of fuels is directly converted into electrical energy are called fuel cells.
$\rightarrow$ The common example of fuel cell is hydrogen-oxygen fuel cell. Fuel cells are different from ordinary galvanic cells.

Fuel cell involves which of the following reaction(s) ?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $O _{2}(g) + 2H _{2}O(l) + 4e^{-} \rightarrow 4OH^{-}(aq.)$ (at cathode)

  2. $O _{2}(g) + 2H _{2}O(l) + 4e^{-}\rightarrow 4OH^{-}(aq.)$ (at anode)

  3. $2H _{2}(g) + 4OH^{-}(aq.) \rightarrow 4H _{2}O(l) + 4e^{-}$ (at anode)

  4. $2H _{2}(g) + 4OH^{-}(aq.) \rightarrow 4H _{2}O(l) + 4e^{-}$ (at cathode)

Show answer
Correct Option: A,C
Explanation:

Question approach,

at anode- loss of electron takes place,
at cathode- gain of electron takes place,
in option B, at anode gain of electron is talking place and in option D at cathode, loss of elctron is taking place;
so, both these statements are wrong
option A and C are representing the Hydrogen fuel cell reactions
hence, both A and C are correct options. 

In a fuel cell the fuel is fed to which compartment?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. Anode compartment

  2. Cathode compartment

  3. Both the compartments

  4. None of the above

Show answer
Correct Option: A
Explanation:

Therefore, it can clearly be said that fuel is fed to the anode compartment.

In _________ cells, reactants are continuously supplied energy which can be withdrawn indefinately until outside supply of reactant is maintained. These cells are more efficient than conventional batteries and moreover, these are eco-friendly. 

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. fuel

  2. galvanic

  3. primary

  4. secondary

Show answer
Correct Option: A
Explanation:

Fuel cell is a device that generates electricity by chemical reaction. Every fuel cell has one positive and one negative electrode called anode and cathode respectively. The reactions that produce electricity take place at electrodes.

In hydrogen fuel cell the catalyst used is/are:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. $Ag$

  2. $Fe$

  3. $Pt$

  4. $Zn$

Show answer
Correct Option: A,C
Explanation:

$Ag$ and $Pt$ being inert are used for catalyst in the fuel cell.

A and C are correct

Which of the following statements regarding fuel cell is (are) true?

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. They have efficiency of about 60-70%

  2. There efficiency is less then conventional methods

  3. They do not cause pollution

  4. They can supply indefinite amount of energy until outside supply of reactants is maintained

Show answer
Correct Option: A,C,D
Explanation:

Fuel cells have efficiency of 60-70%. Reactants, products and catalyst used are non- toxic, thus, they are pollution-free. And they can supply indefinite amount of energy until outside supply of reactants like H$ _{2}$ and O$ _{2}$  is maintained.

In a $H _2 - O _2$ fuel cell, combustion of hydrogen occurs to:

chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

  1. remove adsorbed oxygen from electrode surface

  2. create potential difference between the two electrodes

  3. produce high purity water

  4. generate heat

Show answer
Correct Option: B
Explanation:

Combustion of hydrogen occur in ${ H } _{ 2 }-{ O } _{ 2 }$ fuel cell because of difference in potential between two electrode. So on one electrode oxidation occur while on another reduction.

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