Year 9 Science · Unit 2 · Lesson 14

Combustion of Hydrocarbons

Challenge Worksheet

Name

Date

Class

Learning Goals

Critically evaluate claims about the environmental status of natural gas as a fuel.
Distinguish what combustion chemistry alone tells us from what requires wider evidence.
Identify the data needed to make a scientifically reliable comparison between energy sources.

Go Deeper

Evaluate the claim

Someone claims...

"Natural gas (methane) is a clean fuel because combustion produces only water and no carbon. It should be promoted as a 'green' energy source to replace coal, which produces far more pollution per unit of energy."

(a) What part of this claim is chemically accurate, based on what you have learned about combustion?

Challenge 2 marks

(b) What is misleading or oversimplified in this claim? Identify at least two specific problems with the reasoning.

Challenge 2 marks

(c) What data or evidence would you need to decide whether natural gas is genuinely a 'green' energy source compared to coal and renewables? List at least three pieces of evidence and explain why each matters.

Challenge 3 marks

Show What You Know

1. Complete combustion of methane (CH₄) produces CO₂ and H₂O, while complete combustion of octane (C₈H₁₈) produces 8 mol of CO₂ per mole of fuel. Using this pattern, explain why replacing shorter-chain hydrocarbons with longer-chain ones does not reduce CO₂ emissions, even if both fuels burn completely. Include a reference to the balanced equation in your answer.

Challenge 4 marks

2. NSW Fire and Rescue responds to approximately 3,000 carbon monoxide incidents each year. Evaluate the statement: "CO poisoning incidents could be eliminated if all gas appliances were replaced with electric appliances powered by renewable energy." In your answer, consider both the combustion chemistry and any limitations of this solution.

Challenge 4 marks

Wrap Up

In one sentence, what was the main idea of this lesson?