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.	chemical	because it will burn bread
3.	you forgot to dry the bread knife when you washed it and reddish brown spots appeared on it.	chemical	because rust is a chemical reaction
4.	you blow dry your wet hair.	physical	because its not changing its chemical property
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.
	in a fireworks show, the fireworks explode giving off heat and light.

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

	changing the size and shapes of pieces of wood would be a chemical change.
	evaporation occurs when liquid water changes into a gas.

Explanation:

Scenario 2

Step1: Identify change type

Toasting bread too long causes burning (black bread, smoke). Burning involves new substance (charcoal, smoke) formation, so it's a chemical change.

Step2: Provide evidence

New substances (blackened bread, smoke) are formed, indicating a chemical reaction (combustion).

Step1: Identify change type

Reddish - brown spots on a wet, un - dried knife are rust. Rust is a new substance (iron oxide) formed from iron (knife) reacting with water and oxygen, so it's a chemical change.

Step2: Provide evidence

The formation of rust (a new, reddish - brown substance) on the iron knife shows a chemical reaction between iron, water, and oxygen.

Step1: Identify change type

Blow - drying wet hair only changes water from liquid to gas (evaporation). No new substance is formed, so it's a physical change.

Step2: Provide evidence

The water on hair changes state (liquid to gas) without forming a new substance; it's just drying (physical state change).

Answer:

Physical or Chemical Change? : Chemical
Evidence... : The bread turns black (new substance, charred) and smoke (new gas) is produced, showing a chemical reaction (burning/combustion) occurred.

Scenario 3