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 is 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)

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:

Part B:

Scenario	Physical or Chemical Change?	Evidence...
3. You forgot to dry the bread knife when you washed it and reddish brown spots appeared on it.	Chemical	Reddish-brown rust (new substance) forms on the knife.
4. You blow dry your wet hair.	Physical	Only water changes from liquid to gas; no new substance forms.
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.	Chemical	Baking powder reacts to produce new gas (carbon dioxide) substance.
6. You take out your best silver spoons and notice that they are very dull and have some black spots.	Chemical	Black tarnish (new substance, silver sulfide) forms on the silver.
7. A straight piece of wire is coiled to form a spring.	Physical	Only shape changes; no new substance forms.
8. Food color is dropped into water to give it color.	Physical	No new substance; only mixing of two substances.
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.	Physical; Chemical	Chewing only changes food particle size; enzyme action creates new sugar substances.
10. In a fireworks show, the fireworks explode giving off heat and light.	Chemical	Explosion produces new substances, heat, and light from chemical reactions.

Part C:

1. Changing wood size/shape only alters its physical form, no new substance is made.
2. Physical changes only modify form, not the chemical makeup of matter.
3. Evaporation is the phase change of liquid water to gaseous water vapor.

Answer:

1. F
2. F
3. T