seegongsik
Grade 6 (age 11-12)

grade 6 Physical & Chemical Changes

The ways substances change can be sorted into two big groups: physical changes and chemical changes. In a physical change, like folding paper or melting ice, only the shape or state changes and the substance stays the same. In a chemical change, like paper burning to ash or iron rusting, a new substance with different properties is formed. Press the two buttons in turn to compare ice turning into water with paper turning into ash, and decide by asking whether a new substance has formed.

There are two kinds of change

💡 What is a physical change?
①A change where only the shape or state changes and the substance stays the same.
②When ice melts into water, both are still the same substance, H₂O.
③Torn or folded paper is still paper.
④Sugar dissolved in water is still sugar; evaporate the water and you get the sugar back.

Comparing physical and chemical changes

Comparing changes

Physical and chemical changes
FeaturePhysical changeChemical change
Properties of the substanceStay the sameChange
Turning backUsually easy (water → ice)Usually hard (ash → paper is impossible)
New substanceNone formedFormed
Example 1Ice meltingPaper burning
Example 2Sugar dissolving in waterIron rusting
Example 3Tearing paperCooking an egg

Spotting changes around us

🏠 Physical changes around us
①Laundry drying (water → water vapor)
②A cold window fogging up (water vapor → water)
③Salt dissolving in water
④A glass marble breaking
⑤Only the shape or state changes and the substance stays the same. Some physical changes, like a broken marble, are hard to undo.
🔥 Chemical changes around us
①Food going bad (bacteria break it down)
②Iron rusting (iron and oxygen combine into rust)
③A candle burning (carbon dioxide and water form)
④Toast or rice cakes browning when grilled
⑤A new substance with different properties forms.

Summary

Physical change
Only shape or state changes → the substance stays the same
Usually it can be undone, like ice ↔ water ↔ water vapor.
Chemical change
The substance changes → a new substance forms
Usually it is hard to undo, like paper → ash or iron → rust.
🎯 Key points
①Physical change: only shape or state changes; the substance stays the same.
②Chemical change: a new substance with different properties forms.
③Physical changes are usually easy to undo; chemical changes are usually hard to undo.
④But the surest test is not whether it can be undone, it is whether a new substance has formed.
⑤If a new color, smell, bubbles, light or heat appear, suspect a chemical change.

Examples and Unit Test

Example 1
Is ice melting into water a physical change or a chemical change? Why?
1
Ice and water are the same substance, H₂O; only the state changes from solid to liquid.
2
No new substance forms, so it is a physical change. Freeze the water again and it becomes ice.
▸ A physical change (ice and water are both H₂O, and no new substance forms)
Ice ↔ water ↔ water vapor are all the same substance in different forms.
Example 2
Burning paper produces ash and carbon dioxide, and it cannot be turned back into paper. What kind of change is this, and how do you decide?
1
As the paper burns, ash and carbon dioxide appear that were not there before.
2
A new substance has formed, so it is a chemical change.
▸ A chemical change / test: has a new substance formed?
The test is whether a new substance has formed. Press the chemical change button in the picture and the paper turns into ash.
Unit-test style
Which statement about how substances change is correct?
①Sugar dissolving in water is a chemical change.
②Paper burning to ash is a chemical change.
③No physical change can ever be undone.
④No new substance forms in a chemical change.
⑤Iron rusting is a physical change.
▸ ② Paper burning to ash is a chemical change.
1
Burning paper forms new substances, ash and carbon dioxide, so it is a chemical change.
2
Sugar dissolving is a physical change (①), physical changes can usually be undone (③), a chemical change forms a new substance (④), and iron rusting is a chemical change (⑤).
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