This MCQ module is based on: Physical and Chemical Changes
TOPIC 15 OF 46
Physical and Chemical Changes
🎓 Class 7
Science
CBSE
Theory
Ch 5 — Changes Around Us: Physical and Chemical
⏱ ~14 min
🌐 Language: [gtranslate]
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[myaischool_lt_science_assessment grade_level="class_7" science_domain="chemistry" difficulty="basic"]
Every Moment Something Is Changing!
Look around you for a minute. A piece of ice left on a plate slowly turns into a puddle of water. The little bud on the jasmine plant outside your window opens up into a full, fragrant flower by evening. The glass of cold water you poured from the fridge warms up to room temperature if you forget to drink it. And the bright yellow banana on the kitchen shelf develops brown spots, softens, and finally begins to smell sweet and overripe.
Every one of these is a change — something looked or behaved one way earlier, and now looks or behaves differently. Are all these changes of the same kind? Can we get the original thing back in every case? Let us investigate.
Think first: Ice melted. A flower bloomed. Water warmed up. A banana ripened. Which of these can you undo easily? Which changes seem permanent?
5.1 Types of Changes — Physical or Chemical?
Scientists divide all changes into two broad groups based on what happens to the substance itself.
(a) Physical Change
In a physical change, only outward features like shape, size or state change. The substance remains the very same material. That is why most physical changes can be undone.
- Water becoming ice in the freezer, and ice melting back to water
- Tearing a sheet of paper into small pieces
- Stretching a rubber band
- Dissolving sugar or salt in water (evaporate the water and the solid comes back)
- Folding a handkerchief, cutting vegetables, moulding clay
(b) Chemical Change
In a chemical change, the original material is converted into one or more new substances with different properties. These changes are usually irreversible — you cannot easily get the starting material back.
- Burning a piece of paper → ash + smoke (cannot make paper again from ash)
- Rusting of an iron nail → reddish-brown rust
- Cooking raw rice, baking a cake, boiling an egg
- Milk turning into curd
- A banana ripening or food getting spoilt
Activity 5.1 — Changes at Home L2 Understand
Walk through your kitchen, bathroom and garden with a notebook. List any 10 changes you notice. Mark each one as P (physical) or C (chemical).
Predict: Will you find more physical or more chemical changes at home?
Examples: boiling water (P), frying an egg (C), cutting onions (P), dough rising (C), ice cubes melting (P), burning a matchstick (C), washing clothes (P), curdling milk (C), stretching a dupatta (P), a torn apple browning (C). Most homes show a healthy mix of both!
5.2 How Do We Spot a Chemical Change?
While doing an experiment or observing a change in nature, scientists look for certain signs that hint a new substance has been formed. Any one (or more) of the following gives away a chemical change:
- A change in colour — like an apple slice turning brown, or iron turning reddish after rusting
- A gas is given off — bubbles rising, or a sudden "fizz"
- Heat or light is released, or absorbed — the container becomes warm, cold, or even glows
- A new solid (precipitate) appears in a clear liquid
- A new smell is produced — like the pleasant aroma of roasted peanuts or the sharp odour of spoilt milk
Activity 5.2 — Baking Soda Meets Vinegar L3 Apply
You need: a spoonful of baking soda, some vinegar (sirka), a small glass or bowl.
Steps:
- Place the baking soda in the bowl.
- Slowly pour a little vinegar onto it.
- Watch carefully.
Predict: What will happen when the two mix?
The mixture fizzes and bubbles rise rapidly. The bubbles are made of carbon dioxide (CO₂) gas — a new substance! The evolution of gas tells us this is a chemical change. If you bring a lit matchstick near the bubbles, the flame goes out, confirming the gas is CO₂ (which does not support burning).
Activity 5.3 — Observing a Burning Candle L4 Analyse
With your teacher's help, light a small candle on a plate. Observe the flame, the wax and the wick for two minutes.
Predict: Are all the changes in a burning candle of the same kind?
Two kinds of change happen together! (i) The solid wax near the wick melts into liquid wax — this is a physical change (it can solidify again). (ii) The wax vapour burns in air, producing heat, light, carbon dioxide and water vapour — this is a chemical change. So one candle flame shows both types of changes at once!
Activity 5.4 — Iron + Sulphur, Heated L3 Apply
Set-up (teacher's demo): Mix a little iron filings with yellow sulphur powder on a heat-resistant tile. Touch the mixture with a magnet — it attracts! The sulphur stays behind.
Now heat the mixture strongly in a test tube. The mixture glows red and turns into a black solid called iron sulphide (FeS). Touch it with the magnet again.
Predict: Will the magnet still pick up iron from the black solid?
No! The magnet does not pick up anything from the black iron sulphide. A new substance with completely different properties has been formed. This is a clear chemical change: \(\mathrm{Fe + S \rightarrow FeS}\).
Key idea: If a change produces a new substance with different properties (new colour, gas, precipitate, smell or temperature change), it is a chemical change. If only the shape, size or state changes and the material is still the same, it is a physical change.
Interactive: Physical or Chemical?
Click each change-chip to drop it in the correct box. Correct chips turn green; wrong ones flash red.
Ice melting
Iron rusting
Tearing paper
Burning wood
Dissolving salt in water
Milk turning into curd
Stretching a rubber band
Cooking rice
Physical Change
Chemical Change
Score: 0 / 8
Competency-Based Questions L3 Apply
Rehana helps her mother in the kitchen. She sees her mother grating a carrot into fine shreds, boiling milk until it becomes curd overnight, squeezing a lemon into water, frying puris in hot oil and finally lighting an agarbatti on the shelf.
1. Which of the above is purely a physical change?
(b) — Grating only changes the size/shape of carrot pieces; the substance is still carrot.
2. Name the gas you would smell strongly when the agarbatti is burning. Is burning a chemical or physical change? Justify.
Smoke contains fragrant oils, plus CO₂ and some H₂O vapour. Burning is a chemical change because a new substance (ash + gases) forms that cannot be turned back into the agarbatti stick.
3. When milk turns to curd, two signs of a chemical change appear. Mention them. L4
(i) A new smell (slightly sour) develops, (ii) the taste changes from sweet to sour, and (iii) the liquid milk thickens into a semi-solid — showing a new substance (curd) has formed.
4. Fill in the blank: When iron filings are mixed with sulphur and heated, a black substance called __________ is formed.
Iron sulphide (FeS).
5. Rehana's brother says, "Melting and burning are the same kind of change." Is he right? Explain in 2 sentences.
No. Melting is a physical change — the substance (e.g., wax) is unchanged; solid wax becomes liquid wax and can be solidified again. Burning is a chemical change — new substances (CO₂, water vapour, ash) are produced and cannot be turned back into the original wax.
Assertion–Reason Questions
Choose: (A) Both A and R true, R explains A. (B) Both true, R does not explain A. (C) A true, R false. (D) A false, R true.
A: Mixing baking soda with vinegar is a chemical change.
R: A new gas (carbon dioxide) is evolved during the mixing.
(A) — Evolution of a new gas is a clear sign of a chemical change, so R correctly explains A.
A: Dissolving sugar in water is a physical change.
R: The sugar can be recovered back by evaporating the water.
(A) — The substance (sugar) is unchanged and can be recovered, so the change is physical/reversible.
A: Burning of a candle is only a chemical change.
R: Wax melting near the wick is a physical change.
(D) — A is false (candle burning shows both physical and chemical changes). R is true — wax melting is indeed physical.
Frequently Asked Questions — Physical and Chemical Changes
What does the topic 'Physical and Chemical Changes' cover in Class 7 Science?
The topic 'Physical and Chemical Changes' is part of NCERT Class 7 Science Chapter 5 — Changes Around Us: Physical and Chemical. It covers the key ideas of physical change, chemical change, signs of chemical change, reversible, irreversible, examples, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Physical and Chemical Changes' important for Class 7 NCERT Science?
'Physical and Chemical Changes' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 5 — Changes Around Us: Physical and Chemical — introduces physical change and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Physical and Chemical Changes?
The key concepts in 'Physical and Chemical Changes' for Class 7 Science are: physical change, chemical change, signs of chemical change, reversible, irreversible, examples. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 5 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Physical and Chemical Changes taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Physical and Chemical Changes' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 5 — Changes Around Us: Physical and Chemical — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
What real-life examples of physical change can Class 7 students observe at home?
Class 7 students can observe physical change at home in many simple ways linked to 'Physical and Chemical Changes'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 5 — Changes Around Us: Physical and Chemical. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Physical and Chemical Changes' connect to other chapters of Class 7 Science?
'Physical and Chemical Changes' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of physical change appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 5 — Changes Around Us: Physical and Chemical — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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