Year 7 Science · Unit 2 · Lesson 10
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Learning Goals
Real-world context
When you cook a steak on a barbecue in Australia, many different changes happen at once. The cold meat warms up and becomes firm. Juices evaporate as steam. The surface turns from red–pink to dark brown. Proteins inside the meat change permanently, and new flavour compounds form that weren't in the raw meat. The colour and texture change cannot be reversed by cooling the steak down again.
(a) Identify ONE physical change that occurs when cooking a steak, and explain why it is physical using lesson ideas.
(b) Identify TWO signs that chemical changes are also happening when cooking a steak. For each, name the sign and describe what you observe.
Compare two
Complete the table to compare physical change and chemical change. Fill in both columns for each feature.
| Feature | Physical Change | Chemical Change |
|---|---|---|
| Is a new substance formed? | ||
| Is it usually reversible? | ||
| What happens at the particle level? | ||
| One everyday example | ||
| One everyday example from Australia |
1. A student evaporates seawater and collects the salt left behind. Which type of change is this? Justify your answer by explaining what happens at the particle level.
2. Rusting is considered a chemical change, but breaking a rusty nail in half is a physical change. Explain the difference between these two events using the concept of "new substance".
Wrap Up
In one sentence, what was the main idea of this lesson?