Year 7 Science · Unit 2 · Lesson 11
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Learning Goals
Read the graph
Temperature rise during four exothermic reactions
Data: representative values from standard school chemistry demonstrations (exothermic reactions).
(a) Which reaction produced the largest temperature rise? How much hotter did it get compared to the neutralisation reaction?
(b) All four reactions show a temperature rise. Does this temperature rise alone prove a chemical change has occurred? Give one example from the graph and explain your reasoning.
(c) Beyond temperature change, name TWO other signs of chemical change you would expect to observe when burning wood.
Order the steps
A class is investigating whether vinegar + bicarb soda is a chemical change using the five signs. Number these steps from 1 to 7 to show the correct order of a scientific investigation.
| Order | Step |
|---|---|
| Record all observations: note bubbling, temperature change, any colour change, and whether a precipitate forms. | |
| Write a conclusion: state whether there is evidence for chemical change and which signs were observed. | |
| Set up the equipment: place a beaker on a bench, pour in 50 mL of white vinegar, and place a thermometer in the liquid. | |
| Write a prediction: predict which of the five signs you expect to see and why. | |
| Identify the question: "Is mixing vinegar and bicarb soda a chemical change?" | |
| Add one teaspoon of bicarb soda to the vinegar and watch what happens immediately. | |
| Evaluate your prediction: compare what you predicted with what you actually observed. |
1. During a fireworks display in Sydney on New Year's Eve, you observe bright coloured flashes, loud bangs, and trails of coloured smoke. Identify THREE signs of chemical change present and link each to what you observe.
2. A student boils water and says: "I can see bubbles — this must be a chemical change." Explain the student's error and describe what the bubbles in boiling water actually are.
Wrap Up
In one sentence, what was the main idea of this lesson?