Change Synthesis and Checkpoint 1 Preparation
Today you will connect ideas from Lessons 1–4 in a concept map, find gaps in your understanding, and plan focused revision for Checkpoint 1.
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On paper or in your workbook, draw a concept map using each term below. Connect the terms with labelled arrows so every link forms a sentence you can explain.
Start with these concepts: physical change · chemical change · particles · state change · reactants · products · evidence of a reaction · temperature change · gas or precipitate · reversible
Scaffold: Begin with “A physical change…” and “A chemical change…”. Add at least six labelled arrows, including one link from particles to state change and one from reactants to products. Add a counterexample showing why one clue (such as bubbles or colour change) alone does not prove a reaction.
Check for gaps: Circle any arrow you cannot explain using an example from Lessons 1–4. Write the lesson or idea to revisit, then list two questions you will practise before Checkpoint 1.
Use your completed concept map to review the links you made across Lessons 1–4. Which links were hardest to explain, and what idea do you need to revisit?
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.