Physical vs. Chemical Changes: Same Stuff or New Stuff?
Atlas stands at a wooden workbench in a bright science workshop, holding a crayon in one hand while a candle flame flickers nearby. On the bench sit an ice cube melting in a bowl, a rusty nail, a folded piece of paper, and a small piece of burnt toast — all waiting to be examined and compared.
- Explain the difference between a physical change and a chemical change using your own words.
- Identify whether melting, cutting, burning, or rusting is a physical or chemical change.
- Compare what stays the same and what is different after each type of change.
- Predict whether a new substance is made when a specific change happens to matter.
Key terms
- Physical change
- A change in shape or form, same stuff.
- Chemical change
- A change that makes a brand-new substance.
- Substance
- What a thing is made of.
- Rust
- The new substance made when iron meets air and water.
Same Stuff, New Shape
In a physical change, the shape or size of something changes, but the stuff it is made of stays the same. When you cut paper in half, it is still paper, and you could tape it back together. When an ice cube melts, it becomes liquid water, but it is still water and you can freeze it back. Physical changes move things around or change their form, but they never make a brand-new substance out of the old one.
New Stuff Is Born
In a chemical change, the old substance is gone and a brand-new substance forms instead. When paper burns, you are left with ash and smoke, not paper. When an iron nail rusts, iron joins with oxygen and water in the air to make rust, a different substance. Clues for a chemical change are a new color, a new smell, bubbles of gas, or flames. If you cannot easily get the old stuff back, something new was made.
Worked examples
Is a melting ice cube physical or chemical?
- The ice cube melts and becomes liquid water.
- It is still water, just a different form, and you can freeze it back.
- Since no new substance formed, this is a physical change.
Answer: Melting is a physical change, because the water stays water.
Activity
Sort each change into the correct bin: Physical Change or Chemical Change.
Practice
Is cutting a banana into slices physical or chemical?
Name one clue that a chemical change has happened.
Common mistakes to avoid
- Any big change is a chemical change.A change is only chemical if a brand-new substance forms.
- Hard to undo means it is chemical.The real test is whether a new substance was made, not how hard it is.
Check your understanding
Maria tears a piece of paper into tiny pieces. Which statement BEST describes this change?
A log is placed in a campfire. After a while, only ash and smoke remain. What kind of change happened, and why?
Which of the following is the BEST clue that a chemical change has taken place?
Recap
A physical change alters shape or form but keeps the same substance, like cutting paper or melting ice. A chemical change makes a brand-new substance, like burning paper or rusting iron.
Reflect
What change have you seen that made brand-new stuff?