Changes Around Us: Physical and Chemical explains how substances change in shape, size, state, smell, colour or composition. A physical change forms no new substance, while a chemical change forms one or more new substances.
Important Questions Class 7 Science Chapter 5 help students revise physical changes, chemical changes, combustion, ignition temperature, candle burning, rusting, lime water test, reversible changes, irreversible changes, weathering and erosion.
Class 7 Science Chapter 5 begins with simple observations: ice melts into water, cold water becomes warmer, a bud turns into a flower, and a banana develops brown spots. These examples help students notice that changes happen everywhere.
Key Takeaways from Class 7 Science Chapter 5
| Detail |
Information |
| Chapter Name |
Changes Around Us: Physical and Chemical |
| Class |
7 |
| Subject |
Science |
| Main Concept |
Classification of changes around us |
| Main Types |
Physical change and chemical change |
| Key Reaction |
Lime water turns milky due to carbon dioxide |
| Important Process |
Combustion |
| Important Term |
Ignition temperature |
| Other Concepts |
Reversible changes, desirable changes, weathering, erosion |
Important Questions Class 7 Science Chapter 5 with Answers
These questions cover the main ideas of the chapter. Students should mention the observation, type of change and reason.
Important Questions Class 7 Science Chapter 5: Basic Concepts
Q1. What is a physical change?
A physical change is a change in which only physical properties change. Shape, size, state or appearance may change.
No new substance forms in a physical change. Melting ice, folding paper, boiling water and crushing chalk are examples.
Q2. What is a chemical change?
A chemical change is a change in which one or more new substances form.
Rusting of iron, burning magnesium, curdling of milk, cooking food and mixing vinegar with baking soda are chemical changes. These changes involve chemical reactions.
Q3. What is the main difference between physical and chemical change?
The main difference is the formation of a new substance. A physical change forms no new substance.
A chemical change forms one or more new substances. For example, melting ice gives water, but burning magnesium gives magnesium oxide.
Q4. Why is melting of ice a physical change?
Melting of ice is a physical change because only the state changes. Ice changes from solid water to liquid water.
No new substance forms. The water can become ice again if cooled.
Q5. Why is rusting of iron a chemical change?
Rusting is a chemical change because a new brown substance called rust forms.
Rust is different from iron. It forms when iron reacts with air and moisture over time.
Class 7 Science Chapter 5 Question Answer on Physical Changes
Physical change questions often look simple, but students lose marks when they forget to mention “no new substance”. Use that phrase in every answer.
Q1. Why is folding paper a physical change?
Folding paper is a physical change because only the shape changes. The paper remains paper.
If the paper is unfolded, the same sheet can be obtained again. No new substance forms.
Q2. Why is inflating a balloon a physical change?
Inflating a balloon is a physical change because the rubber sheet only changes shape and size.
When air escapes, the balloon can return close to its earlier form. The material of the balloon remains the same.
Q3. Is crushing chalk a physical change?
Yes, crushing chalk is a physical change. The chalk changes from a solid piece into powder.
The substance remains chalk. Only its size and shape change.
Q4. Is boiling water a physical or chemical change?
Boiling water is a physical change. Water changes from liquid state to vapour state.
No new substance forms. The vapour can condense back into liquid water.
Q5. Is cutting vegetables a physical change?
Cutting vegetables is a physical change because only size and shape change.
No new substance forms at the moment of cutting. However, later decay of vegetables is a chemical change.
Class 7 Science Chapter 5 Question Answer on Chemical Changes
Chemical changes need stronger reasoning. Students should look for new substances, gas formation, colour change, smell change, heat, light or permanent change.
Q1. Why is lime water turning milky a chemical change?
Lime water turns milky when carbon dioxide reacts with it. A new white substance called calcium carbonate forms.
This new substance makes the liquid appear cloudy. So, the change is chemical.
Q2. What happens when vinegar reacts with baking soda?
Vinegar reacts with baking soda and produces carbon dioxide gas. Students observe bubbles and fizzing.
Since a new gas forms, this is a chemical change. The gas can turn lime water milky.
Q3. Why is burning magnesium ribbon a chemical change?
Burning magnesium ribbon is a chemical change because magnesium reacts with oxygen.
A new white powder called magnesium oxide forms. Heat and light also come out during the reaction.
Q4. Why is curdling of milk a chemical change?
Curdling of milk is a chemical change because milk changes into curd, which has different properties.
The original milk cannot return by simple physical methods. New substances form during the process.
Q5. Why is composting a chemical change?
Composting is a chemical change because food waste and leaves decompose due to bacteria and fungi.
New substances form during decomposition. The compost has different properties from the original waste.
Physical and Chemical Changes Class 7: Difference with Examples
Students should learn the difference through examples, not only definitions. The easiest test is to check whether a new substance forms.
| Basis |
Physical Change |
Chemical Change |
| New substance |
No new substance forms |
One or more new substances form |
| Property changed |
Shape, size, state or appearance |
Composition and properties change |
| Example |
Melting ice |
Rusting of iron |
| Reversibility |
Often reversible |
Often irreversible |
| Daily-life example |
Folding clothes |
Cooking food |
Physical Change and Chemical Change Difference Class 7 Questions
Q1. Give two examples of physical changes.
Melting of ice and boiling of water are physical changes. In both cases, only the state changes.
Ice, water and water vapour are different states of the same substance.
Q2. Give two examples of chemical changes.
Rusting of iron and burning of wood are chemical changes. In both cases, new substances form.
Rust is different from iron. Ash, smoke and gases are different from wood.
Q3. Can one process involve both physical and chemical changes?
Yes, one process can involve both physical and chemical changes.
Burning a candle is an example. Wax melts and evaporates, which are physical changes. Wax vapour burns and forms new substances, which is a chemical change.
Combustion Class 7 Science Important Questions
Combustion is one of the most important sections of this chapter. Students should remember oxygen, fuel and ignition temperature together.
Q1. What is combustion?
Combustion is a chemical reaction in which a substance reacts with oxygen and produces heat or light.
Wood, paper, cotton, kerosene and candle wax are combustible substances. They can burn under suitable conditions.
Q2. What are combustible substances?
Combustible substances are substances that can burn. They undergo combustion.
Examples include wood, paper, cotton, kerosene and wax. These substances need oxygen and enough heat to start burning.
Q3. What three things are needed for combustion?
Combustion needs three things: fuel, oxygen and heat.
Fuel is the combustible substance. Oxygen supports burning. Heat helps the fuel reach its ignition temperature.
Q4. Why does a candle under an inverted glass tumbler stop burning?
The candle stops burning because the oxygen supply becomes limited.
A candle needs oxygen for combustion. Once the available oxygen gets used, the flame goes out.
Q5. How can lime water prove that carbon dioxide forms during candle burning?
Lime water turns milky in the presence of carbon dioxide.
When a candle burns, carbon from wax reacts with oxygen and produces carbon dioxide. This gas turns lime water milky.
Ignition Temperature Class 7 Questions
Ignition temperature questions test whether students understand why a substance does not burn automatically in air.
Q1. What is ignition temperature?
Ignition temperature is the lowest temperature at which a substance catches fire.
A substance burns only after it reaches this temperature. That is why paper can stay in air but burns when heated enough.
Q2. Why does paper catch fire when sunrays are focused through a magnifying glass?
The magnifying glass focuses sunrays on a small spot. This heats the paper strongly.
When the paper reaches its ignition temperature, it starts burning.
Q3. Is air alone enough for combustion?
No, air alone is not enough for combustion. A combustible substance also needs heat.
For example, paper does not burn just because it lies in air. It burns only when it reaches its ignition temperature.
Q4. Why does a lighted matchstick burn paper quickly?
A lighted matchstick has a temperature higher than the ignition temperature of paper.
When it touches paper, the paper quickly reaches the temperature needed to burn.
Q5. How can fire be put out if someone’s clothes catch fire?
The person should be wrapped with a blanket or cloth that is not synthetic.
This cuts off the air supply. Without oxygen, combustion stops.
Class 7 Science Chapter 5 MCQ with Answers
Class 7 Science Chapter 5 MCQ questions cover direct concepts, activities and application-based ideas. Read each option carefully before selecting the answer.
Q1. Which change forms no new substance?
(a) Rusting
(b) Burning wood
(c) Melting ice
(d) Curdling milk
Answer: (c) Melting ice
Melting ice changes only the state of water.
Q2. Which change is chemical?
(a) Folding paper
(b) Boiling water
(c) Burning magnesium
(d) Rolling a mat
Answer: (c) Burning magnesium
Burning magnesium forms magnesium oxide.
Q3. Lime water turns milky due to:
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Water vapour
Answer: (b) Carbon dioxide
Carbon dioxide reacts with lime water and forms calcium carbonate.
Q4. The lowest temperature at which a substance catches fire is called:
(a) Freezing point
(b) Boiling point
(c) Ignition temperature
(d) Melting point
Answer: (c) Ignition temperature
Ignition temperature is needed for combustion.
Q5. Which substance is combustible?
(a) Wood
(b) Water
(c) Sand
(d) Glass
Answer: (a) Wood
Wood can burn in the presence of oxygen and enough heat.
Q6. Which change can be reversed?
(a) Ripening of fruit
(b) Rusting of iron
(c) Melting of ice
(d) Making popcorn
Answer: (c) Melting of ice
Melted water can be frozen again.
Q7. Burning of a candle involves:
(a) Only physical change
(b) Only chemical change
(c) Both physical and chemical changes
(d) No change
Answer: (c) Both physical and chemical changes
Wax melts physically, while wax vapour burns chemically.
Q8. Weathering of rocks helps form:
(a) Plastic
(b) Soil
(c) Glass
(d) Wax
Answer: (b) Soil
Weathering breaks and changes rocks over time, leading to soil formation.
Class 7 Science Chapter 5 Extra Questions and Answers
Class 7 Science Chapter 5 extra questions and answers help students prepare for reasoning and competency-based tests.
Q1. Why does blowing into lime water make it milky?
Exhaled air contains carbon dioxide. Carbon dioxide reacts with lime water and forms calcium carbonate.
Calcium carbonate is an insoluble white substance. It makes lime water appear milky.
Q2. What happens when baking soda is mixed with water?
Baking soda dissolves in water, but no strong fizzing occurs.
This is different from mixing baking soda with vinegar or lemon juice. In those cases, carbon dioxide forms due to a chemical reaction.
Q3. Why is making popcorn from corn irreversible?
Making popcorn is irreversible because the corn changes permanently in shape, texture and structure.
The original corn cannot be obtained again. So, this change cannot be reversed.
Q4. Why is ripening of fruit a chemical change?
Ripening of fruit is a chemical change because its colour, smell, taste and softness change.
New substances form inside the fruit during ripening. The raw fruit cannot return to its earlier form.
Q5. Why is drying wet clothes a physical change?
Drying wet clothes is a physical change because water only evaporates from the clothes.
No new substance forms. Water vapour can condense back into liquid water.
Q6. Why is burning wood a chemical change?
Burning wood is a chemical change because new substances such as ash, smoke and gases form.
The original wood cannot be obtained again. Heat and light also come out.
Reversible and Irreversible Changes Class 7 Questions
This part of the chapter helps students connect change with real-life outcomes. Reversible does not always mean physical, but many simple reversible changes are physical.
Q1. What are reversible changes?
Reversible changes are changes in which the original substance or object can be obtained again.
Melting ice and boiling water are reversible changes. Water can freeze again, and water vapour can condense again.
Q2. What are irreversible changes?
Irreversible changes are changes in which the original substance or object cannot be obtained again.
Cooking food, making popcorn, rusting iron and ripening fruit are examples. These changes cannot return to the original form easily.
Q3. Is dissolving sugar in water reversible?
Dissolving sugar in water can be reversed by evaporating the water.
The sugar can be recovered after water leaves. So, this change can be considered reversible under suitable conditions.
Q4. Is grinding wheat grains into flour reversible?
Grinding wheat grains into flour is not reversible in a practical way.
The original grains cannot be obtained again from flour. So, this is an irreversible physical change.
Q5. Is stitching cloth into a shirt reversible?
Stitching cloth into a shirt can be partly reversed by removing stitches.
However, the cut cloth pieces cannot return to the original uncut cloth. So, students may explain that it is not fully reversible.
Weathering and Erosion Class 7 Important Questions
Weathering and erosion help students see that changes can happen slowly in nature. These questions also connect science with geography.
Q1. What is weathering of rocks?
Weathering is the breaking down and changing of rocks due to natural factors.
Temperature changes, tree roots, freezing water, air and water can cause weathering. Weathering helps form soil over time.
Q2. Is weathering a physical or chemical change?
Weathering can involve both physical and chemical changes.
Rocks may break into smaller pieces, which is physical. Their minerals may react with air or water, which is chemical.
Q3. What is erosion?
Erosion is the movement of broken rock pieces, soil and sediments by wind or flowing water.
River rocks become smooth due to constant erosion. Erosion during landslides is a physical change.
Q4. How does weathering help in soil formation?
Weathering breaks large rocks into smaller particles. Chemical changes can also alter the rock surface.
Over long periods, these particles help form soil. This process may take thousands of years.
Q5. Why are many natural changes slow?
Many natural changes are slow because rocks, sediments and landscapes change little by little.
Weathering, erosion and soil formation take long periods. They often cannot be reversed in a short time.
Activity-Based Questions from Changes Around Us Physical and Chemical Class 7
Activity-based answers should mention observation, inference and conclusion.
Q1. A student blows air into tap water and lime water. What will happen?
In tap water, only bubbles appear. The water does not show a major visible change.
In lime water, the liquid turns milky. This shows that exhaled air contains carbon dioxide.
Q2. Vinegar and baking soda are mixed, and the gas is passed through lime water. What is the gas?
The gas is carbon dioxide. It turns lime water milky.
The formation of this gas shows that vinegar and baking soda undergo a chemical change.
Q3. A covered candle goes out after some time. What does this prove?
This proves that oxygen is necessary for combustion.
When the candle is covered, the supply of oxygen becomes limited. The flame stops after using the available oxygen.
Q4. Wax melts near a candle flame. Is this a physical change?
Yes, melting wax is a physical change. Wax changes from solid to liquid.
No new substance forms during melting. However, burning wax vapour is a chemical change.
Q5. Lemon juice writing turns brown when heated. Is this change reversible?
No, the change is not easily reversible. Heating causes a chemical change in the lemon juice and paper surface.
The dark brown letters cannot return to the invisible form by cooling.
Competency-Based Questions on Changes Around Us
These questions test whether students can apply the rule “Has a new substance formed?” to new situations. Write the observation first, then the reason.
Q1. A student leaves an iron nail near a window during the rainy season. After a few days, it develops a brown coating. What type of change is this?
This is a chemical change because a new substance called rust forms.
Rainy air has moisture. Iron reacts with air and moisture to form rust.
Q2. A student tears a sheet of paper into small pieces. Has a new substance formed?
No new substance forms. The paper only changes in size and shape.
So, tearing paper is a physical change, even if it is difficult to restore the original sheet.
Q3. A matchstick is struck and starts burning. Which conditions helped combustion?
The matchstick had fuel and oxygen from air. Striking produced enough heat.
When it reached ignition temperature, combustion started.
Q4. A student mixes vinegar and baking soda and observes bubbles. What should the student conclude?
The student should conclude that a chemical change occurred.
The bubbles show that a new gas formed. That gas is carbon dioxide.
Q5. A wet floor dries after some time. Is this a chemical change?
No, it is a physical change.
Water evaporates from the floor. No new substance forms during evaporation.
Long Answer Questions from Class 7 Science Chapter 5
Long answers should have a clear definition, example and reason. Add textbook activity examples where possible.
Q1. Explain physical and chemical changes with examples.
A physical change affects only physical properties such as shape, size, state or appearance. No new substance forms.
Examples include melting ice, folding paper, boiling water, drying wet clothes and crushing chalk. In these cases, the substance remains the same.
A chemical change forms one or more new substances. The new substances have different properties.
Examples include rusting of iron, burning magnesium, curdling milk, cooking food and mixing vinegar with baking soda.
The main test is simple: if no new substance forms, the change is physical. If a new substance forms, the change is chemical.
Q2. Explain the lime water test for carbon dioxide.
The lime water test helps detect carbon dioxide gas. When carbon dioxide passes through lime water, the lime water turns milky.
This happens because carbon dioxide reacts with calcium hydroxide in lime water. A new white substance called calcium carbonate forms.
This substance is insoluble in water. That is why the solution looks cloudy or milky.
The test appears in two activities. Exhaled air turns lime water milky. Gas from vinegar and baking soda also turns lime water milky.
Q3. Explain combustion and the conditions needed for it.
Combustion is a chemical reaction in which a substance reacts with oxygen and gives heat or light.
A substance that burns is called a combustible substance. Wood, paper, cotton, kerosene and wax are examples.
Three things are necessary for combustion. These are fuel, oxygen and heat.
Fuel is the substance that burns. Oxygen supports burning. Heat raises the fuel to its ignition temperature.
If any one condition is removed, combustion stops. A covered candle stops burning because oxygen supply ends.
Q4. Why does burning a candle involve both physical and chemical changes?
A burning candle shows both physical and chemical changes.
The wax near the flame melts. Liquid wax rises through the wick and evaporates due to heat. Melting and evaporation are physical changes.
The wax vapour then burns in air. This produces heat, light, carbon dioxide and water vapour.
New substances form during burning. So, that part is a chemical change.
This example helps students understand that one process can involve more than one type of change.
Q5. Explain desirable and undesirable changes with examples.
Desirable changes are changes that are useful in a situation. Cooking food, changing milk into curd, ripening fruits and composting food waste can be desirable.
Undesirable changes are harmful or unwanted in a situation. Rusting of iron and decay of stored food are undesirable.
The same change may be useful in one situation and harmful in another. Food decomposition is harmful when stored food spoils.
But decomposition is useful when food waste becomes compost. This shows that the usefulness of a change depends on the situation.