Year 12 / Ethanol production and hydrogen fuel cells

Two routes to energy.

Fermentation converts glucose to ethanol and carbon dioxide using enzymes from yeast under suitable warm, anaerobic conditions. Hydrating ethene uses steam and an acid catalyst. Compare feedstock renewability, energy demands, rate and product separation.

A hydrogen fuel cell converts a continuous supply of hydrogen and oxygen to water while transferring electrons through a circuit. In acidic conditions: H₂ → $2H^{+}$ + $2e^{-}$ and O₂ + $4H^{+}$ + $4e^{-}$ → 2H₂O.

In alkaline conditions: H₂ + 2OH⁻ → 2H₂O + $2e^{-}$ and O₂ + 2H₂O + $4e^{-}$ → 4OH⁻. Both give the same overall reaction after electron and ion cancellation. The environmental impact also depends on how hydrogen is produced.

INTERACTIVE MODEL

Fuel in. Electrical energy out.

Anode: H₂ → 2H⁺ + 2e⁻. Cathode: ½O₂ + 2H⁺ + 2e⁻ → H₂O.

Schematic hydrogen–oxygen fuel cell. Electrons flow from the anode through the external circuit to the cathode. The electrolyte transports ions, not electrons.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ 2H₂ + O₂ → 2H₂O

Assumed knowledge

Half-equations must balance atoms and charge before being combined.

Learning checkpoints & source

YOUR SYLLABUS CHECKPOINT

Compare fermentation and ethene hydration.
Write acidic and alkaline fuel-cell half-equations.
Explain electron transfer in a fuel cell.

QCAA Chemistry 2025 v1.3 · p. 42 ↗

READY TO TRY IT?

Two routes to energy.

Fuel in. Electrical energy out.

Turn the idea into an answer.