Matter, Changes, and Simple Chemical Ideas
Changes in matter
Physical changes
A physical change changes the form of matter without making a new substance. Examples include melting, freezing, cutting, and dissolving. The material is still the same substance after the change.
Chemical changes
A chemical change produces one or more new substances. Signs can include color change, gas formation, heat release, or the formation of a solid called a precipitate. Rusting is a chemical change.
Which is a chemical change?
Rusting creates a new substance called iron oxide.
Correct answer: Rusting iron
Physical vs. chemical change
Physical change
- No new substance is formed
- Often reversible
- Example: melting
Chemical change
- New substance is formed
- Often harder to reverse
- Example: burning
Mixtures and pure substances
A pure substance contains only one kind of material. A mixture contains two or more substances together. Air is a mixture of gases, and salad is a mixture of ingredients.
Which is a mixture?
Air contains several gases mixed together.
Correct answer: Air
Simple chemistry words
How to think about changes
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Step 1: Observe what changes
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Step 2: Ask whether a new substance formed
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Step 3: Decide whether the change is physical or chemical
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Step 4: Record evidence for your choice
What is the main difference between a physical change and a chemical change?
That distinction is the key idea.
Correct answer: A chemical change makes a new substance; a physical change does not.
Give one example of a mixture.
Any correct mixture example is acceptable.
Correct answer: Air, salad, or soil.