1.3.4—Biofuels
- Syllabus
- First assessment 2025
- Objective
- 1.3.4
- Level
- SL
Biofuels as Renewable Fuels
Biofuels are renewable when their carbon is replenished through biological carbon fixation, such as photosynthesis, on a relevant timescale.
Evaluate both sides: possible benefits include renewable supply and lower net carbon or sulfur emissions; disadvantages include land competition with food production and other production impacts. State the evidence for each claim.
Test a carbon-neutral claim with a life-cycle boundary: count cultivation, fertilizer, processing, transport, land-use change and combustion, then credit carbon taken up during regrowth on the relevant timescale. Renewable describes replenishment, not automatically low impact or zero net emissions.
Evaluating Biofuel Advantages and Disadvantages
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Outline two advantages of using ethanol as a fuel instead of gasoline (petrol).
Any two:
«ethanol is» renewable / sustainable resource
«ethanol has» low/zero carbon footprint / produces less CO2
less sulfur dioxide «than fossil fuels»
OR
less acid rain «than fossil fuels»
less incomplete combustion «than fossil fuels»
OR
less carbon monoxide/soot «than fossil fuels»
Marking guidance:
Accept "ethanol is biodegradable /less toxic than gasoline".
Do not accept just "less harmful".
2 max
Combustion and Thermodynamics Summary
Retrieve the route: identify complete or incomplete combustion products, compare fuels and biofuels, balance fuel-cell half-equations, calculate ΔS° and ΔG°, then use ΔG, Q and K to reason about spontaneity and equilibrium.
Check products before balancing, evidence before evaluation, oxidation versus reduction, kelvin and unit consistency, the sign of ΔG, and whether Q is below, equal to, or above K.