Change Synthesis and Checkpoint 1 Preparation
In 2020, CSIRO published findings showing Year 8 students who made concept maps improved test scores by 23%, today you'll build exactly that kind of map before Checkpoint 1.
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At the start of this lesson, you mapped out everything you'd learned in Lessons 1–4 and spotted where your understanding still felt a bit shaky.
Looking back at that map now, which gaps did this lesson help you close? What big idea feels most solid for you heading into Checkpoint 1?
1. Which of the following is a physical change?
2. What is the best evidence that a chemical reaction has occurred?
3. In the particle model, what happens when a solid is heated?
4. Which term describes a reaction that releases heat?
5. What is a precipitate?
6. Which of these is NOT a state of matter?
7. Boiling water is an example of:
8. What is condensation?
9. Which particles move the fastest?
10. Why is rusting classified as a chemical change?
Explain the difference between a physical change and a chemical change, giving one example of each. (3 marks)
Describe the particle model and use it to explain what happens when ice melts. (4 marks)
Model answers (click to reveal)
SAQ 1 (3 marks)
Model answer: A physical change changes only the appearance, shape or state of a substance, and no new substance is made, so the same particles are still present and the change can usually be reversed. For example, melting wax changes solid wax into liquid wax, but it is still wax. A chemical change produces one or more new substances with different properties, the original particles are rearranged into new ones, and it is usually very hard to reverse. For example, burning paper turns it into ash, smoke and gases that cannot be turned back into paper. The key difference is that a physical change makes no new substance, while a chemical change does.
SAQ 2 (4 marks)
Model answer: The particle model states that all matter is made of tiny particles that are always moving. In a solid such as ice, the particles are packed closely in a fixed, regular arrangement and can only vibrate on the spot because of strong forces holding them together. When ice is heated, the particles absorb energy and gain kinetic energy, so they vibrate faster and more strongly. Once they have enough energy, the forces holding them in fixed positions are partly overcome, so the particles break free from their rigid arrangement and begin to slide past one another. The ice has now melted into liquid water, where the particles are still close together but can move around, which is why the water can flow and take the shape of its container.