Class 7 Science · Original EZT practice
Changes Around Us: Physical and Chemical (Class 7 Chapter 5): summary and practice
Ice melts, buds open, bananas spot and iron rusts - change is everywhere, and this chapter teaches you to sort it. The one big question: did anything new get made? If no new substance appears, the change is physical; if a new substance forms, it is chemical. Everything else - rusting, burning, reversibility, and whether a change is welcome - builds on that one test. All questions are original EZT tutor practice following the chapter's own section order.
10 original worked examples, 10 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 18 October 2026:
1. The one big test: is a new substance formed?
In a physical change, only appearance changes - shape, size or state - and no new substance is formed. In a chemical change, one or more new substances are formed through a chemical reaction.
2. Rusting and combustion: two famous chemical changes
Rusting is iron slowly reacting with air and moisture to form rust. Combustion is burning: a substance combines with oxygen, gives off heat and light, and forms new substances.
3. Both at once: the burning candle
Many processes mix the two types. In a burning candle, the melting and evaporation of wax are physical changes, while the burning of wax vapour is a chemical change.
4. Reversible or permanent? Desirable or not?
Some changes can be undone and some cannot. Some changes are welcome and some are not. Desirability depends on our use, not only on the chemistry.
5. Slow natural changes: weathering of rocks
Rocks crack and crumble as water, wind, temperature swings and living things work on them. Physical weathering breaks rock apart; chemical weathering changes the rock material itself.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Apply the new-substance test
Choose the method: Ask what is present after the change, not what the change looks like.
EZT practice question
Classify: (i) melting an ice cube (ii) browning of a cut apple.
Show the worked solution
- Melted ice is still water; only the state has changed.
- No new substance forms, so melting is physical.
- A cut apple turns brown because reaction with air forms a new brown substance.
Answer: Melting an ice cube is a physical change; browning of a cut apple is a chemical change.
Check: The first change can be reversed by freezing; the browning cannot simply be wiped away to restore the apple.
Watch for this: Do not judge by how dramatic the change looks; judge by whether a new substance forms.
Now try it yourself
Classify: dissolving salt in water.
Check your answer
Physical.
The salt can be recovered by evaporating the water.
Explain why boiling is not chemical
Choose the method: Identify the bubbles before deciding whether a new substance formed.
EZT practice question
Students say, "Boiling water is a chemical change because bubbles form." Are they right?
Show the worked solution
- The bubbles are water vapour, not a new gas.
- Water vapour is still water in the gas state.
- No new substance appears during boiling.
Answer: No. Boiling is a physical change because water only changes state.
Check: The vapour can condense back into liquid water.
Watch for this: Bubbles alone do not prove a chemical reaction; identify what is inside them.
Now try it yourself
Classify: baking a cake.
Check your answer
Chemical.
Heat drives reactions that form new substances; the cake cannot be unbaked.
Sort common physical changes
Choose the method: Check whether the original material can be recovered by a simple physical step.
EZT practice question
Classify: tearing paper, melting wax and dissolving sugar in water.
Show the worked solution
- Torn paper is still paper, only in smaller pieces.
- Melted wax is still wax and can solidify again.
- Dissolved sugar can be recovered by evaporating the water.
Answer: All three are physical changes because no new substance forms.
Check: Each original substance remains the same substance after the change.
Watch for this: Do not call dissolving a disappearance; the solute is still present in the solution.
Now try it yourself
Is cutting fruit a reversible change?
Check your answer
No.
You cannot rejoin the pieces into the original fruit, although the change is still physical.
Explain rusting without flames
Choose the method: Use formation of a new substance, not fire, as the test for a chemical change.
EZT practice question
Why is rusting a chemical change even though no fire is involved?
Show the worked solution
- Iron reacts slowly with air and moisture.
- The product is rust, a new substance different from iron.
- A chemical change can be slow; it does not need flames.
Answer: Rusting is chemical because rust is a new substance formed from iron, air and moisture.
Check: Rusting cannot be undone by simple drying or wiping.
Watch for this: Do not reserve the word chemical only for fast or fiery reactions.
Now try it yourself
Name the two things iron needs in order to rust.
Check your answer
Air (oxygen) and moisture.
Both are needed for rust to form.
Classify burning magnesium
Choose the method: Compare the white ash with the original metal and note the energy released.
EZT practice question
When magnesium ribbon burns, a white ash forms. Physical or chemical?
Show the worked solution
- Magnesium combines with oxygen as it burns.
- The white ash is a new substance, not magnesium.
- Heat and light are also released.
Answer: Chemical change.
Check: The ash cannot be turned back into magnesium ribbon by a simple physical step.
Watch for this: Do not focus only on the bright flame; the decisive evidence is the new substance.
Now try it yourself
What two forms of energy does combustion usually release?
Check your answer
Heat and light.
Combustion is an energy-releasing reaction with oxygen.
Split a burning candle into physical and chemical parts
Choose the method: Track the wax first as it melts and evaporates, then as its vapour burns.
EZT practice question
List the physical and chemical parts of a burning candle.
Show the worked solution
- Solid wax melts into liquid wax - physical.
- Liquid wax evaporates into wax vapour - physical.
- Wax vapour burns, forming new substances and releasing heat and light - chemical.
Answer: Melting and evaporation of wax are physical changes; burning of wax vapour is a chemical change.
Check: The same everyday event contains both types of change.
Watch for this: Do not label the entire candle event only physical or only chemical.
Now try it yourself
Give one other everyday process where physical and chemical changes happen together.
Check your answer
Cooking - water evaporates physically while ingredients react and brown chemically.
Different parts of one process can follow different change types.
Classify changes as desirable or undesirable
Choose the method: Ask whether the change helps the purpose at hand; chemistry alone does not decide.
EZT practice question
Classify by desirability: (i) iron gate rusting (ii) grapes fermenting for juice or jam-making (iii) fruit ripening (iv) food spoiling in storage.
Show the worked solution
- Rusting weakens the gate, so it is undesirable.
- Controlled fermentation is desirable when done on purpose.
- Fruit ripening is desirable before eating.
- Food spoiling in storage is undesirable.
Answer: (i) undesirable, (ii) desirable, (iii) desirable, (iv) undesirable.
Check: The same broad chemical process can be welcome in one setting and unwanted in another.
Watch for this: Do not assume every chemical change is harmful; many useful changes are chemical.
Now try it yourself
Name one desirable chemical change in the kitchen.
Check your answer
Curd setting, cooking or baking.
Each forms new substances that we want for food.
Separate reversible from permanent changes
Choose the method: Imagine undoing the change by cooling, drying or another simple step.
EZT practice question
Classify as reversible or not: freezing water, setting curd, melting wax and burning paper.
Show the worked solution
- Frozen water can melt back into water - reversible.
- Curd cannot be turned back into milk - not reversible.
- Melted wax can solidify - reversible.
- Burning paper forms ash, gases and smoke - not reversible.
Answer: Reversible: freezing water and melting wax. Not reversible: setting curd and burning paper.
Check: The reversible examples involve only state changes; the others form new substances.
Watch for this: Reversibility is a separate question from speed; a slow change can still be permanent.
Now try it yourself
Is tearing paper reversible?
Check your answer
No.
The pieces cannot be restored to the original sheet by a simple physical change.
Identify physical weathering
Choose the method: Check whether the rock pieces have become a different substance.
EZT practice question
Water seeps into a rock crack, freezes, and widens the crack. Physical or chemical weathering?
Show the worked solution
- Freezing water expands and pushes the crack wider.
- The rock breaks into smaller pieces.
- Those pieces are still the same rock; no new substance forms.
Answer: Physical weathering.
Check: Breaking apart without changing composition is physical.
Watch for this: Do not call every natural outdoor change chemical; look for new substances.
Now try it yourself
How is chemical weathering different from the freezing example?
Check your answer
Chemical weathering changes the rock's composition and forms new substances.
The rock material itself is altered, not just broken.
Explain why weathering is easy to miss
Choose the method: Connect the size and speed of the change to human timescales.
EZT practice question
Why can weathering change a landscape even though we rarely see it happening?
Show the worked solution
- Water, wind, temperature swings and living things act on rocks every day.
- Each effect is small, but it repeats over very long periods.
- Over many years, small cracks and chemical changes add up.
Answer: Weathering is slow and repeated, so its tiny effects accumulate into visible landscape changes.
Check: The explanation uses both slowness and repetition.
Watch for this: Do not expect a rock wall to weather at the speed of ice melting or paper burning.
Now try it yourself
Name one agent of weathering.
Check your answer
Water, wind, temperature change or living things.
All four can help break down or alter rocks.
Try a mixed set
Choose a method or explanation before opening each answer.
1. What is the test for a chemical change?
Show answer and reason
A new substance forms.
Appearance alone can change in a physical change too.
2. Is rusting physical or chemical?
Show answer and reason
Chemical.
Rust is a new substance different from iron.
3. Which part of a burning candle is physical?
Show answer and reason
Melting and evaporation of wax.
The wax remains wax in a different state.
4. What is weathering?
Show answer and reason
The slow breakdown of rocks by water, wind, temperature and living things.
It can involve both physical and chemical changes.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Classify melting butter and burning toast.
- Why is boiling water physical but cooking rice chemical?
- Give one desirable and one undesirable chemical change.
- Why is freezing water in a rock crack physical weathering?
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Questions about this practice page
- What is the simplest way to tell a physical change from a chemical one?
- Ask: is a new substance formed? No new substance means physical, as in melting, dissolving or tearing. A new substance means chemical, as in burning, rusting or curdling.
- Is melting wax a chemical change?
- No - melted wax is still wax and will solidify back. Only when wax vapour burns does a chemical change occur.
- Why is rusting considered a chemical change?
- Because rust is a new substance, chemically different from the iron it came from, and the change is not undone by simple means.
- Can one process involve both kinds of change?
- Yes - in a burning candle, melting and evaporation of wax are physical, while burning of the vapour is chemical.
- Are these the NCERT exercise questions for Changes Around Us?
- No. EZT pages are original practice on this chapter - use them to prepare for the textbook exercises, not as a substitute for your book.