Electrochemical Cells

Concept: Faraday’s law: where = number of electrons transferred.

Step 1: Write electrode reaction.


Step 2: Determine electrons required.
1 mole Mg requires 2 moles of electrons:

Step 3: Calculate charge.

Concept: Kolbe electrolysis produces alkane and CO .

Step 1: Reaction.

Concept: Nernst equation:

Step 1: Identify


Step 2: Reaction quotient


Step 3: Apply Nernst equation
Final Conclusion:
Option (B)

Step 1: Identify Electron Requirement
From the balanced reaction: 1 mole of requires 4 moles of electrons.

Step 2: Use Faraday's Law
where number of moles of electrons,

Step 3: Substitute Values


Step 4: Calculate Charge


Step 5: Express in Faradays


Step 6: Final Answer

Step 1: Understanding the Concept:
Fuel cells, like the hydrogen-oxygen fuel cell, convert chemical energy directly into electrical energy. The reactions at the electrodes (oxidation of fuel and reduction of oxygen) often have high activation energies and proceed slowly at normal temperatures. Catalysts are required to increase the rate of these electrode reactions and improve the overall efficiency of the cell.

Step 2: Key Formula or Approach:
Recall factual knowledge regarding the composition of electrodes in standard fuel cells discussed in typical chemistry curricula.

Step 3: Detailed Explanation:
In a typical fuel cell, the electrodes are made of porous carbon. To make the cell operate efficiently, a catalyst is incorporated into these porous electrodes.
Finely divided transition metals are commonly used for this purpose because of their excellent catalytic properties, specifically their ability to adsorb reactant gases and facilitate electron transfer.
The most frequently used catalysts to enhance the efficiency of fuel cell electrodes are:
- Platinum (Pt)
- Palladium (Pd)
- Finely divided Silver (Ag) is also sometimes used.
Among these, Platinum is the most standard and widely cited answer in educational materials for catalyzing both the anode and cathode reactions in hydrogen fuel cells.

Step 4: Final Answer:
Metals like Platinum (Pt) or Palladium (Pd) are added as catalysts to make fuel cells more efficient.