Year 10 Science · Unit 2 · Lesson 16

Chemical Reactions and the Environment

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Learning Goals

Trace the because-chain from CO₂ combustion to ocean acidification to reef ecosystem collapse.
Compare petrol, ethanol, and hydrogen fuels using evidence from the lesson.
Explain why "zero emission at the exhaust" does not always mean zero carbon overall.

Warm Up

Because… chain

Fill in the missing effects. Each cause leads to the next step. The first and last steps are given.

Fossil fuels burn, large amounts of CO₂ enter the atmosphere

→

CO₂ dissolves in seawater: CO₂ + H₂O → H₂CO₃

→

Ocean pH falls from 8.2 → 8.1 (30% more acidic)

→

Shell-forming organisms struggle to build calcium carbonate

→

Coral bleaching events become more frequent and severe

→

Reef ecosystem collapses, loss of biodiversity and fisheries

Overall outcome:

Your Turn

Real-world context

Australia is exploring alternatives to petrol-powered transport. Queensland already blends 10% ethanol (E10) into petrol at the pump, sourced mainly from sugarcane grown in North Queensland. Several Australian states are investing in hydrogen refuelling infrastructure, while the CSIRO is developing hydrogen technology for domestic and export use. In 2023, there were approximately 20,000 electric vehicles on Australian roads, but hydrogen fuel cell vehicles remain rare.

(a) Compare petrol and sugarcane ethanol as transport fuels. Your answer should address CO₂ emissions and net carbon footprint for each fuel. Use chemical equations or word equations to support your comparison.

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(b) Hydrogen fuel cells produce only water vapour. Explain why hydrogen from natural gas (steam methane reforming) is NOT truly zero-carbon, even though the vehicle itself emits no CO₂.

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Wrap Up

In one sentence, explain why the source of a fuel matters just as much as what the fuel produces when it burns.