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

1. umm! a student removes a loaf of bread hot from the oven. the student cuts a slice off the loaf and spreads butter on it. physical
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. physical
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)

1. changing the size and shapes of pieces of wood would be a chemical change.
2. in a physical change, the makeup of matter is changed.
3. evaporation occurs when liquid water changes into a gas.

Explanation:

Step1: Recall definitions

A physical change is a change in the form or appearance of a substance without changing its chemical composition. A chemical change results in a new substance being formed.

Step2: Analyze Scenario 2

Toasting bread too long causes it to burn. Burning is a chemical reaction that produces new substances (like carbon from the charred bread), so it is a chemical change. Evidence: Formation of black - charred substance and smoke (new substances).

Step3: Analyze Scenario 3

The reddish - brown spots on the bread knife are rust. Rusting is a chemical reaction between iron in the knife, oxygen, and water to form iron oxide. Evidence: Formation of iron oxide (rust), a new substance.

Step4: Analyze Scenario 4

Blowing dry wet hair only changes the state of water from liquid to gas. The hair and water remain chemically the same. Evidence: No new substances are formed, just a change in water's state.

Step5: Analyze Scenario 5

Baking powder reacting to release carbon dioxide bubbles is a chemical reaction. New substances (carbon dioxide) are formed, causing the dough to rise. Evidence: Release of carbon dioxide gas, a new substance.

Step6: Analyze Scenario 6

The dullness and black spots on silver spoons are due to tarnishing. Tarnishing is a chemical reaction between silver and sulfur - containing compounds in the air to form silver sulfide. Evidence: Formation of silver sulfide, a new substance.

Step7: Analyze Scenario 7

Coiling a wire to form a spring only changes the shape of the wire. The wire's chemical composition remains the same. Evidence: No new substances are formed, just a change in shape.

Step8: Analyze Scenario 8

Dropping food color into water is a physical change. The food color disperses in the water, but no new chemical substances are formed. Evidence: No chemical reaction occurs, just a mixture.

Step9: Analyze Scenario 9

Chewing food is a physical change as it only breaks the food into smaller pieces. The changing of starch into sugars by enzymes is a chemical change as new substances (sugars) are formed. Evidence for physical: Change in size of food particles. Evidence for chemical: Formation of sugars.

Step10: Analyze Scenario 10

Fireworks exploding and giving off heat and light is a chemical reaction. New substances are formed during the explosion. Evidence: Release of heat, light and formation of new substances.

Step11: Analyze Part C - 1

Changing the size and shape of pieces of wood is a physical change, not a chemical change. So it is False.

Step12: Analyze Part C - 2

In a physical change, the makeup of matter is not changed. So it is False.

Step13: Analyze Part C - 3

Evaporation of liquid water into gas is a physical change and it occurs when water changes state. So it is True.

Answer:

Scenario	Physical or Chemical Change?	Evidence
3	Chemical	Formation of rust (iron oxide)
4	Physical	No new substances formed, change in water's state
5	Chemical	Release of carbon dioxide gas
6	Chemical	Formation of silver sulfide
7	Physical	No new substances formed, change in shape
8	Physical	No chemical reaction, just a mixture
9	Physical (chewing), Chemical (starch - to - sugar)	Physical: Change in food particle size; Chemical: Formation of sugars
10	Chemical	Release of heat, light and formation of new substances
Part C - 1	False	Changing size/shape of wood is physical change
Part C - 2	False	Makeup of matter is unchanged in physical change
Part C - 3	True	Evaporation is a physical change of water state