VCE Chemistry — Unit 3 AOS 1
Fuel Cells — Flashcards & Quiz
Fuel cells convert chemical energy directly into electrical energy by continuously feeding fuel and oxidant into separate half-cells, and they sit squarely in VCE Chemistry Unit 3 Area of Study 1 — "What are the current and future options for supplying energy?" You need to write the half-equations for hydrogen and methanol fuel cells in both acidic and alkaline electrolytes, balance them carefully, and compare fuel cells with galvanic cells (no exhaustion of reactants) and combustion engines (higher efficiency, fewer pollutants). Examiners often ask you to evaluate fuel cells in a sustainability context.
Key Points
- A fuel cell converts chemical energy directly into electrical energy through continuous feeding of fuel (anode) and oxidant (cathode).
- Hydrogen fuel cell: 2H₂ + O₂ → 2H₂O, with acidic electrolyte: anode 2H₂ → 4H⁺ + 4e⁻, cathode O₂ + 4H⁺ + 4e⁻ → 2H₂O.
- Unlike galvanic cells, fuel cells don't run out — fuel is continuously supplied and products removed.
- Higher energy efficiency than combustion engines (fewer energy conversion steps) and fewer pollutants (water is the only product for H₂ cells).
- Drawbacks: hydrogen production is energy-intensive (most comes from steam reforming of methane today), storage is challenging, and platinum catalysts are expensive.
- VCAA exam skill: write half-equations for H₂ and methanol fuel cells in both acidic and alkaline electrolytes; evaluate against sustainability criteria.
Common Mistakes to Avoid
- Writing fuel cell half-equations without state symbols — always include (g), (l), (aq).
- Forgetting to balance electrons between half-equations before combining.
- Confusing fuel cells (continuous fuel + oxidant feed) with batteries (fixed reactants).
- Omitting water (product or reactant, depending on electrolyte) from acidic fuel cell equations.
- Treating fuel cells as 100% efficient — real efficiency is ~40-60% due to irreversibilities and heat losses.
Exam Strategy
VCAA Unit 3 AOS 1 fuel cell questions ask you to write balanced half-equations and compare efficiency/sustainability with alternatives. For half-equations: identify the fuel (oxidised at anode) and oxidant (reduced at cathode), then balance atoms, charges, and electrons. For sustainability, discuss hydrogen production methods, storage challenges, and lifecycle emissions.
Sample Flashcards
Q1: How does a hydrogen fuel cell work?
A fuel cell is a galvanic cell that converts chemical energy into electrical energy with a continuous supply of reactants, so it does not run down while fuel is supplied. Common design features: porous electrodes, which give a large surface area for gaseous reactants to contact the electrolyte and allow products to escape, increasing efficiency; catalysts in the electrodes to speed up the reactions; and an electrolyte (acidic, basic or a polymer membrane) to conduct ions. In an acidic hydrogen fuel cell: anode H₂(g) → 2H⁺(aq) + 2e⁻; cathode O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l).
Q2: How are Faraday’s laws applied to galvanic and fuel cells?
Faraday’s laws link the charge passing through a cell to the amount of reactant used or product formed. Charge Q = I × t (current in A, time in s). Moles of electrons n(e⁻) = Q ÷ F, where the Faraday constant F = 96 500 C mol⁻¹. The half-equation gives the mole ratio between electrons and the reactant or product. The steps can be reversed to find the current or time needed to use or produce a given amount.
Sample Quiz Questions
Q1: A hydrogen fuel cell stores hydrogen gas inside the cell for later use.
Answer: FALSE
Fuel cells do NOT store fuel — they require a continuous external supply of hydrogen and oxygen. They convert chemical energy to electrical energy as long as fuel is supplied, unlike batteries which store a fixed amount of energy.
Q2: If the current drawn from a fuel cell is doubled for the same length of time, the amount of hydrogen consumed also doubles.
Answer: TRUE
Q = It, so doubling the current doubles the charge and the moles of electrons (n = Q/F). The half-equation fixes the ratio of H₂ to electrons, so twice as much hydrogen is used.
Revision Tip
Half-equation balancing is procedural — use Revizi flashcards to drill hydrogen, methanol, and methane fuel cells in both acidic and alkaline electrolytes.
Related Concepts
Last updated: 9 October 2026 · 2 sample flashcards · 2 sample quiz questions