Physical and Chemical Changes

Name:

Date:

Part 1: Key Ideas and Vocabulary

1. Complete the definitions.

A physical change changes the ____________________ or state of a substance, but does not make a new substance.

A chemical change produces one or more ____________________ substances with different properties.

2. Match each term with its correct meaning.

A. Reactant

B. Product

C. Reversible change

D. Irreversible change

1. A substance formed during a chemical reaction

2. A change that can be undone

3. A starting substance in a chemical reaction

4. A change that is difficult or impossible to undo

Answers: A–____ B–____ C–____ D–____

3. Which statement best describes a chemical change?

The substance changes size only.

A new substance is formed.

The substance changes from solid to liquid.

The substance is moved to a different container.

Part 2: Classifying Changes

4. Write P for physical change or C for chemical change.

a. Ice melting: ____

b. Paper burning: ____

c. Water evaporating: ____

d. An apple turning brown: ____

e. A piece of wood being cut: ____

f. Iron rusting: ____

5. Select all the observations that could be evidence of a chemical reaction.

Gas bubbles form.

A new colour appears.

A solid precipitate forms.

A substance is cut into smaller pieces.

Heat or light is produced.

6. Explain why melting chocolate is a physical change.

7. Explain why burning wood is a chemical change. Include one piece of evidence.

Part 3: Practical Investigation — Vinegar and Bicarbonate

Aim: To investigate the reaction between vinegar and sodium bicarbonate.

Equipment: Small plastic cup, 50 mL vinegar, 2 teaspoons sodium bicarbonate, teaspoon, tray, safety glasses and thermometer.

Safety: Wear safety glasses. Do not taste the substances. Keep the mixture away from eyes and mouth. Wash hands after the investigation. Work in a well-ventilated area.

Method:

1. Place the cup on a tray and pour in 50 mL of vinegar.

2. Measure two teaspoons of sodium bicarbonate.

3. Predict what will happen, then add the sodium bicarbonate to the vinegar.

4. Observe the reaction for two minutes. Record the starting and final temperature if a thermometer is available.

5. Dispose of the mixture as instructed by your teacher and clean the equipment.

8. Prediction: What do you think will happen when the two substances are mixed?

9. Observation record

Starting temperature: __________ °C Final temperature: __________ °C

Gas bubbles or fizzing: ________________________________________________

Other observations: ____________________________________________________

10. Conclusion and higher-order thinking

Was the reaction a physical or chemical change? Use two observations to justify your answer.

Higher-order question: How could you design a fair test to investigate whether using more sodium bicarbonate changes the amount of gas produced?

Teacher Answer Key

1. shape; new. 2. A–3, B–1, C–2, D–4. 3. A new substance is formed.

4. a P, b C, c P, d C, e P, f C.

5. Gas bubbles form; a new colour appears; a solid precipitate forms; heat or light is produced.

6. Melting changes chocolate from solid to liquid, but it remains the same substance and can be cooled to solidify again.

7. Burning wood forms new substances, such as ash and gases. Evidence may include heat, light, smoke or a colour change.

8–10. Answers will vary. Expected observations include fizzing and gas bubbles, and possibly a temperature change. The reaction is chemical because new substances, including carbon dioxide gas, are formed. A fair test should change only the amount of sodium bicarbonate, keep the vinegar volume and concentration constant, and measure the gas produced in the same way.