Physical and Chemical Changes

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Date:

Part 1: Understanding Changes

1. Complete the definitions.

A physical change alters the __________ or state of a substance, but no new substance is formed.

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

2. Match each term with its meaning by writing the correct letter.

1. Reactant

2. Product

3. Reversible change

4. Irreversible change

A. A substance made during a reaction

B. A change that can be undone

C. A starting substance in a reaction

D. A change that is difficult or impossible to undo

3. Classify each example as a physical change or a chemical change. Write P or C.

a) Ice melting: ____ b) Toast burning: ____ c) Cutting paper: ____

d) An iron gate rusting: ____ e) Sugar dissolving in water: ____

4. Select all the observations that could provide evidence of a chemical reaction.

A new colour appears

A gas forms and bubbles are produced

A substance is cut into smaller pieces

A temperature change occurs

A solid precipitate forms

5. Explain why melting chocolate is usually a physical change, while burning chocolate is a chemical change.

Part 2: Practical Investigation — Vinegar and Bicarbonate

Aim: To investigate the changes that occur when vinegar reacts with sodium bicarbonate.

Equipment: Small plastic cup, 50 mL vinegar, 1 tablespoon sodium bicarbonate, balloon, funnel, measuring cylinder and safety glasses.

Safety: Wear safety glasses. Do not taste the materials. Keep the mixture away from eyes and mouth. Wash hands after the investigation. Tell your teacher about spills.

Method: Measure 50 mL of vinegar into the cup. Use the funnel to place one tablespoon of sodium bicarbonate into the balloon. Carefully stretch the balloon over the cup without tipping in the powder. Lift the balloon so the powder falls into the vinegar. Observe and record what happens.

6. Write a prediction for what you think will happen when the two substances are mixed. Include a reason.

7. Record your observations.

Before mixing: Colour and appearance of vinegar: ________________________________

Appearance of sodium bicarbonate: ______________________________________________

After mixing: Bubbles or gas: ________________________________________________

Temperature change or other evidence: ___________________________________________

What happened to the balloon? ___________________________________________________

8. Write a conclusion. Was this mainly a physical change or a chemical change? Use evidence from your observations.

9. Higher-order question: The balloon inflated during the reaction. Explain what this suggests about the substances produced.

Answer Key

1. Shape; new.

2. 1–C, 2–A, 3–B, 4–D.

3. a) P, b) C, c) P, d) C, e) P.

4. A new colour appears; gas or bubbles are produced; a temperature change occurs; a solid precipitate forms.

5. Melting chocolate changes its state or shape but does not make a new substance. Burning chocolate forms new substances, such as gases and char, so it is a chemical change.

6. Answers will vary. A suitable prediction is: “I predict that bubbles will form and the balloon will inflate because a gas may be produced.”

7. Answers will vary. Expected observations include fizzing, bubbles, a temperature change and the balloon inflating.

8. This is a chemical change because gas was produced and the reaction showed evidence of forming new substances.

9. The balloon inflated because a gas was produced during the reaction. This gas takes up space and is different from the starting substances.