Year 9 Science · Unit 2 · Lesson 11
Challenge Worksheet
Learning Goals
What if…?
Scenario
Natural gas, mostly methane (CH₄), is piped from offshore fields in the Bass Strait to Melbourne and across southeastern Australia. In August 2026, a major pipeline rupture cuts off methane supply to 400,000 homes for an estimated three months. Engineers propose substituting propane (C₃H₈) from existing LPG storage tanks in regional Victoria to maintain heating and cooking supply. A Year 9 student says: "Propane and methane are both alkanes, they have the same kinds of bonds, so we can just use propane in the same appliances, right?"
Using what you know from this lesson, predict and explain what would happen if propane were used directly in appliances designed for methane. In your answer: compare the boiling points and physical state of both alkanes at room temperature; compare their energy content (propane releases more energy per mole than methane); and evaluate whether the substitution would work safely and efficiently. Use scientific terms.
1. Use the general formula CₙH₂ₙ₊₂ to determine the molecular formula of the alkane with 10 carbon atoms (decane). Show your working clearly, then predict whether decane is a gas, liquid, or solid at room temperature (approximately 20 °C) and justify your prediction using the trend in boiling points along the alkane homologous series.
2. A student claims: "All alkanes are flammable, so methane and butane are equally dangerous to use as fuel." Evaluate this claim. In your answer, identify what is correct, explain what is misleading, and use the trend in flammability across the alkane series to justify your evaluation.
Wrap Up
In one sentence, what was the main idea of this lesson?