Tag: electrochemistry, rechargeable batteries, and fuel cells

Quizzes (0) Questions (20)

Questions Related to electrochemistry, rechargeable batteries, and fuel cells

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

The overall reaction of a hydrogen-oxygen fuel cell is:

  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. $4OH^- _{(aq)}+4e^-\rightarrow 2H _2O _{(l)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
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: $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$

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

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

  1. mercury cell

  2. danicell cell

  3. fuel cell

  4. lead storage cell
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Which of the following statements is true for 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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

The efficiency of a fuel cell is given by:

  1. $\frac{\Delta S}{\Delta G}$
  2. $\frac{\Delta H}{\Delta G}$
  3. $\frac{\Delta G}{\Delta S}$
  4. $\frac{\Delta G}{\Delta H}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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}$
Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

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 

  1. 80%

  2. 87%

  3. 90%

  4. 97%
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

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

  1. $ -0.1624\,JK^{-1}$
  2. $ -162.4\,JK^{-1} $
  3. $ +162.4\,JK^{-1} $
  4. $ +0.1624\,JK^{-1} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The question asks for the standard entropy change of a fuel cell reaction at 25°C but does not specify the reaction. Without knowing the specific fuel cell reaction (e.g., H2/O2, methanol, etc.), the value cannot be verified. The magnitude -162.4 JK^-1 is plausible for a multi-electron process like hydrogen oxidation but requires reaction context.