Year 8 Science · Unit 3 · Lesson 6

Heating, Cooling and Change of State

Challenge Worksheet

Name

Date

Class

Learning Goals

Apply the relationship between pressure and boiling point to a real-world scenario.
Distinguish between the temperature of boiling and what boiling means physically.
Evaluate whether a physical change classification holds under altered conditions.

Go Deeper

What if…?

Scenario

Mount Everest stands at 8,849 m above sea level, where atmospheric pressure is roughly 34 kPa — about one-third of the pressure at sea level (101 kPa). At this altitude, water boils at approximately 70°C instead of 100°C. Members of a 2023 Australian mountaineering expedition found that their freeze-dried meal packets required almost twice the stated cooking time, even though the water was bubbling vigorously in the pot. The team's doctor also warned that drinking "boiling" water from the pot was not enough to kill all harmful pathogens.

Using what you know from this lesson, predict and explain what would happen in this scenario. Address all three of the following in your answer: (1) Why is the boiling point of water only 70°C on Everest? (2) How does this affect cooking time? (3) Is "boiling" at 70°C still a physical change? Justify your answer using the particle model.

Challenge 4 marks

Show What You Know

1. A heating curve for water shows a flat plateau at 100°C. On Everest, at what temperature would you expect this plateau to appear? Explain why the plateau still exists, even though the temperature is lower.

Challenge 3 marks

2. The doctor on the expedition said that boiling water at 70°C might not kill all pathogens. Using your understanding of how temperature affects chemical and biological processes, explain why lower boiling temperatures create a food safety problem that doesn't exist at sea level.

Challenge 3 marks

Wrap Up

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