Question

part b
read each scenario. decide whether a physical or chemical change has occurred and give evidence for your decision. the first one has been done for you to use as an example.

scenario	physical or chemical change?	evidence...
2. your friend decides to toast a piece of bread, but leaves it in the toaster too long. the bread is black and the kitchen if full of smoke.
3. you forgot to dry the bread knife when you washed it and reddish brown spots appeared on it.
4. you blow dry your wet hair.
5. in baking biscuits and other quick breads, the baking powder reacts to release carbon dioxide bubbles. the carbon dioxide bubbles cause the dough to rise.
6. you take out your best silver spoons and notice that they are very dull and have some black spots.
7. a straight piece of wire is coiled to form a spring.
8. food color is dropped into water to give it color.
9. chewing food to break it down into smaller particles represents a ________ change, but the changing of starch into sugars by enzymes in the digestive system represents a ________ change.
10. in a fireworks show, the fireworks explode giving off heat and light.

part c: true (t) or false (f)

2. in a physical change, the makeup of matter is changed.
3. evaporation occurs when liquid water changes into a gas.
4. evaporation is a physical change.
5. burning wood is a physical change.
6. combining hydrogen and oxygen to make water is a physical change.
7. breaking up concrete is a physical change.
8. sand being washed out to sea from the beach is a chemical change.
9. when ice cream melts, a chemical change occurs.
10. acid rain damaging a marble statue is a physical change.

Explanation:

Step1: Recall physical - chemical change definitions

Physical change: No new substances formed, change in state or appearance. Chemical change: New substances formed, often with color - change, gas evolution, heat release etc.

Step2: Analyze Scenario 2

Bread turning black and smoke formation indicate new substances (charcoal and combustion products) are formed. So it's a chemical change. Evidence: New substances (charcoal) formed, smoke evolved.

Step3: Analyze Scenario 3

Reddish - brown spots on the knife are rust (iron oxide), a new substance formed from iron in the knife and oxygen in air. So it's a chemical change. Evidence: New substance (rust) formed, color change.

Step4: Analyze Scenario 4

Blowing dry wet hair only changes water from liquid to gas state. No new substances formed. So it's a physical change. Evidence: No new substances, change of water state.

Step5: Analyze Scenario 5

Baking powder reacting to release carbon - dioxide bubbles means new substances (carbon dioxide) are formed. So it's a chemical change. Evidence: Gas evolution, new substance (carbon dioxide) formed.

Step6: Analyze Scenario 6

Silver spoons getting dull and black spots are due to formation of silver sulfide. New substance formed. So it's a chemical change. Evidence: New substance (silver sulfide) formed, color change.

Step7: Analyze Scenario 7

Coiling a wire to form a spring only changes its shape. No new substances formed. So it's a physical change. Evidence: No new substances, shape change.

Step8: Analyze Scenario 8

Food color dissolving in water is a physical mixing. No new substances formed. So it's a physical change. Evidence: No new substances, just mixing.

Step9: Analyze Scenario 9

Chewing food is physical (breaking into smaller pieces). Changing starch to sugars by enzymes is chemical (new substances - sugars formed). Evidence for physical: No new substances, size change. Evidence for chemical: New substances (sugars) formed.

Step10: Analyze Scenario 10

Fireworks exploding giving off heat and light means new substances are formed during combustion. So it's a chemical change. Evidence: Heat and light release, new substances formed.

Step11: Analyze Part C - Statement 1

Changing size and shape of wood is a physical change. So the statement is False.

Step12: Analyze Part C - Statement 2

In a physical change, matter's makeup is not changed. So the statement is False.

Step13: Analyze Part C - Statement 3

Evaporation of water from liquid to gas is correct. So the statement is True.

Step14: Analyze Part C - Statement 4

Evaporation is a physical change. So the statement is True.

Step15: Analyze Part C - Statement 5

Burning wood is a chemical change. So the statement is False.

Step16: Analyze Part C - Statement 6

Combining hydrogen and oxygen to make water is a chemical change. So the statement is False.

Step17: Analyze Part C - Statement 7

Breaking up concrete is a physical change. So the statement is True.

Step18: Analyze Part C - Statement 8

Sand being washed out to sea is a physical change. So the statement is False.

Step19: Analyze Part C - Statement 9

Ice - cream melting is a physical change. So the statement is False.

Step20: Analyze Part C - Statement 10

Acid rain damaging a marble statue is a chemical change. So the statement is False.

Answer:

Scenario	Physical or Chemical Change?	Evidence
3	Chemical	New substance (rust) formed, color change
4	Physical	No new substances, change of water state
5	Chemical	Gas evolution, new substance (carbon dioxide) formed
6	Chemical	New substance (silver sulfide) formed, color change
7	Physical	No new substances, shape change
8	Physical	No new substances, just mixing
9	Physical (chewing); Chemical (starch - to - sugar)	Physical: No new substances, size change; Chemical: New substances (sugars) formed
10	Chemical	[SSE onError error]