What distinguishes a fuel cell from a galvanic cell such as a dry cell or lead-acid battery?
- A fuel cell continuously converts chemical energy directly into electrical energy, whereas galvanic cells convert chemical energy into electrical energy but are typically used until the reactants are exhausted - VCE - SSCE Chemistry - Question 5 - 2006 - Paper 1
Question 5
What distinguishes a fuel cell from a galvanic cell such as a dry cell or lead-acid battery?
- A fuel cell continuously converts chemical energy directly into elect... show full transcript
Worked Solution & Example Answer:What distinguishes a fuel cell from a galvanic cell such as a dry cell or lead-acid battery?
- A fuel cell continuously converts chemical energy directly into electrical energy, whereas galvanic cells convert chemical energy into electrical energy but are typically used until the reactants are exhausted - VCE - SSCE Chemistry - Question 5 - 2006 - Paper 1
Step 1
What distinguishes a fuel cell from a galvanic cell such as a dry cell or lead-acid battery?
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Answer
A fuel cell continuously converts chemical energy directly into electrical energy, whereas galvanic cells convert chemical energy into electrical energy but are typically used until the reactants are exhausted. Fuel cells have reactants (like hydrogen and oxygen) that are supplied continuously, which allows them to operate under steady conditions, unlike conventional galvanic cells. The products of fuel cells (usually water) are not accumulated, allowing for efficient and ongoing reactions.
Step 2
On the diagram above
i. in circles A and B, indicate the polarity of the cathode and anode
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Answer
Circle A represents the cathode and Circle B represents the anode.
Step 3
ii. show, by using an arrow, the direction of electron flow in the external circuit.
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Answer
Electrons flow from the anode (B) to the cathode (A) in the external circuit.
Step 4
Write an equation for each of the following reactions.
i. the overall cell reaction
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Answer
The overall reaction is:
2H2+O2→2H2O
Step 5
ii. the reaction at the cathode
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The reaction at the cathode is:
O2+4e−+2H2O→4OH−
Step 6
i. How much electrical energy, in joules, would be provided by the cell?
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Answer
The energy provided is given by the formula:
Energy=Current×Voltage×Time
Thus, substituting the values:
Energy=0.500×0.600×(10×60)=180 joules
Step 7
ii. Calculate the charge, in coulombs, produced by the cell.
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Answer
The charge produced can be calculated by:
Q=I×t
Substituting the given values:
Q=0.500×(10×60)=300 coulombs
Step 8
iii. If this particular cell operated at 60.0% efficiency, what amount of hydrogen gas (H₂), in mole, would be consumed by the fuel cell?
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Answer
First, calculate the effective energy output. Given the efficiency:
Effective Energy=Energy×Efficiency=180×0.60=108 joules
The molar energy of hydrogen gas is approximately 286 kJ/mol (or 286,000 J/mol). Thus, the amount of hydrogen consumed is:
n=286000Effective Energy=286000108 moles of H2
