Samacheer Kalvi 7th Science Term 2 Solutions Chapter 3 Pdf
Tamilnadu Board Samacheer Kalvi 7th Science Term 2 Solutions Chapter 3: Tamilnadu State Board Solution Class 7 Science Term 2 Chapter 3 – Changes Around Us.
Samacheer Kalvi 7th Science Term 2 Solutions Chapter 3: Overview
Board |
Samacheer Kalvi |
Class |
7 |
Subject |
Science |
Chapter |
3 |
Chapter Name |
Changes Around Us |
Samacheer Kalvi 7th Science Term 2 Solutions Chapter 3 Pdf
I.) Choose the best answer
1.) When a woolen yarn is knitted to get a sweater, the change can be classified as
___ .
a.) physical change
b.) chemical change
c.)endothermic change
d.) exothermic change
Answer : a. physical change
Solution : Physical changes are the changes in which only physical properties of a substance undergo a change and there is no change in its chemical composition.
2.) _____ of the following are endothermic changes.
a.) Condensation and melting
b.) Condensation and freezing
c.) Evaporation and melting
d.) Evaporation and freezing
Answer : b. Condensation and melting
Solution : Changes in which heat is absorbed are known as endothermic changes eg : condensation and melting process of water.
3.) The chemical change is ____ .
a.) water to clouds
b.) growth of a tree
c.) cow dung to bio-gas.
d.) ice-cream to molten ice-cream.
Answer : c. cow dung to bio-gas
Solution : Changes that occur with the formation of new substance with different chemical composition or transformation of a substance into another substance with the evolution or absorption of heat or light energy are termed as chemical changes.
4.) ____is an example of a periodic change.
a.) Earthquake.
b.) Formation of rainbow in sky
c.) Occurrence of tides in seas.
d.) Showering of rain
Answer : a. Earthquake
Solution : Changes that repeat themselves after a definite interval of time are called periodic changes.
5.) ___ is not a chemical change.
a.) Dissolution of ammonia in water
b.) Dissolution of carbon-di-oxide in water
c.) Dissolution of oxygen in water
d.) Melting of polar ice caps
Answer : d. Melting of polar ice-caps
Solution : Changes that occur with the formation of new substance with different chemical composition or transformation of a substance into another substance with the evolution or absorption of heat or light energy are termed as chemical changes.
II.) Fill in the blanks
1.) Filling up a balloon with hot air is a __physical__ change.
2.) Stretching gold coin into a ring is a _physical ___ change.
3.) Opening a gas cylinder knob converts liquid_ fuel into __gaseous __ fuel. This is an example of__ chemical_change.
4.) Spoiling of food is a _chemical change___.
5.) Respiration is a _exothermic chemical__ change.
III.) True or False. If false, give the correct answer.
1.) Cutting of cloth is an example of a periodic change.
Answer : False
Correct Statement : Cutting of cloth is an example of a physical change.
2.) Taking a glass of water and freezing it by placing it in the freezer is a chemical change.
Answer : False
Correct Statement : Taking a glass of water and freezing it by placing it in the freezer is a physical change.
3.) A bean plant collecting sunlight and turning it into bean seeds is an example of physical and non-periodic change.
Answer : False
Correct Statement : A bean plant collecting sunlight and turning it into bean seeds is an example of chemical and non-periodic change.
4.) If the chemical properties of a substance remain unchanged and the appearance or shape of a substance changes it is called a periodic change.
Answer : False
Correct Statement : If the chemical properties of a substance remain unchanged and the appearance or shape of a substance changes it is called a fossil change.
5.) Tarnishing of silver is an example of endothermic change.
Answer : False
Correct Statement : Tarnishing of silver is an example of exothermic change.
IV) Match the following
A | B | C |
Melting | Change of state from liquid to solid | Ice cube to water |
Condensation | Change of state from liquid to gas | Steam to water drops |
Evaporation | Change of state from solid to liquid | Water to steam |
Freezing | Change of state from gas to liquid | Formation of ice cube |
Periodic change | Occurs at regular time intervals | Ticking of clock |
Non-periodic change | Occurs at irregular time interval | Collecting Flowers |
V.) Classify the following changes as physical and chemical changes
A rough piece of wood is sanded and polished resulting in change in texture, Rusting of a iron nail, Painting the grill, Bending a paper clip, Pounding silver into thin plate, Rolling the chappathi dough into thin wire, Occurrence of day and night, eruption of volcano, burning of matchstick, dosa from the batter, blinking of eyelids, occurrence of a thunderstorm, rotation of the earth, formation of eclipses.
Answer :
Physical changes | Chemical changes |
Bending a paper clip. | Rusting of a iron |
Pounding silver into thin plate. | Eruption of volcano |
Rolling a chapathi dough into thin wire. | Burning of matchstick. |
Occurrence of a day and night. | |
Blinking of eyelids. | |
Occurrence of a thunderstorm. | |
Rotation of the earth. | |
Formation of eclipses. | |
Painting the grill. | |
A rough piece of wood is sanded and polished resulting in change in texture. | |
Dosa from the batter. |
VI.) Analogy
1.) Physical Change: Boiling::Chemical Change: __Burning_.
2.) Wood to saw dust:_Physical change_ :: Wood to Ash: Chemical change
3.) Forest fire: _Non-periodic__ change::Change in period in a school: periodic change
VII.) Very short answer type question
1.) State two examples of periodic changes.
Answer : i) Rotation and Revolution of earth
ii) beating of the heart
2.) Mention any two exothermic reactions.
Answer : i) Burning of magnesium ribbon
ii) Burning of wood
3.) Cold milk is heated and it becomes hot. Which type of change it is?
Answer : Reversible type of change.
4.) What type of change is artificial ripening of fruit?
Answer : Irreversible chemical change
5.) What type of change is colouring of a paper?
Answer : Physical change
6.) Growing of nails is a periodic change. Why?
Answer : Periodic change.
Periodic change occurs periodically at regular intervals . Growing ofnail is a example periodic change
7.) What type of energy changes is associated when ice melts?
Answer : Endothermic – heat is absorbed during the process.
VIII.) Short answer type question
1.) Distinguish physical and chemical changes.
Answer :
Physical changes | Chemical changes |
No new substance is formed | New product is formed |
change is reversible | change is irreversible |
changes do not involve the production of energy | changes usually involve the production of energy [ heat, light, sound etc ] |
change occur in physical properties like shape , size etc . | change occur in chemical composition . |
2.) How can a change occur in a substance?
Answer : A change in a substance refers to an alteration in physical properties ( state, colour, shape etc) or alteration in the composition of matter(chemical change). For example, melting of ice, rusting of iron, ripening of fruit etc.
3.) Can you suggest a method to collect water from sea water?
Answer : Evaporation is a method to collect water from sea water.
4.) Is solar eclipse a periodic change? Give your reason.
Answer : Yes, solar eclipse is a periodic change as it occurs after a definite interval of time.
5.) What is the difference between dissolution of sugar and burning of sugar?
Answer : In dissolution of sugar, sugar disappear in water and convert into sugar solution. From sugar solution , sugar can extract by removing water by the process of evaporation. Dissolution of sugar is a physical change whereas, In burning of sugar sugar undergo chemical reaction with oxygen and smoke and energy release. In the new product is formed therefore this is irreversible chemical change.
IX.) Long answer type question
1.) Explain the following statement: Digestion is a chemical change.
Answer : The food we eat undergo different process in our body. In mouth the food breaks down in small pieces and in stomach and intestines food reacts with chemical and form products which are irreversible .Thats why Digestion is a chemical change.
2.) How the iron blade is fixed into a wooden handle in tools used to dig the soil?
Answer : The iron blade is fixed into a wooden handle by heating the hole of the iron blade. On getting sufficient amount of heat the hole expands and one end of the wooden handle is inserted into the hole easily. On cooling the hole of the iron blade get contracted and it grips the wooden handle tightly.
X.) Higher order Thinking questions
1.) Peeled and unpeeled banana does not look the same. Does that mean peeling banana is a chemical change?
Answer : When banana is peeled it exposed to air. It reacts with the gases in the air and changes colour.Therefore, the peeled banana undergoes a chemical change. As the unpeeled banana is does not react with air because of protective skin on it.
2.) A very hot glass on putting in cold water cracks. What does this change indicate?
Answer : A very hot glass is in an expanded state. When cold water is put in it the hot glass shrinks suddenly. As a result it cracks. This is a physical change not a chemical change as the crack sound is due to change in the temperature of glass not any composition.
3.) Boiling of water is a physical change; but boiling of egg is a chemical change. Why?
Answer : During boiling of water, water changes its state from liquid to gaseous (steam). Change in the state of the substance is known as physical change therefore, boiling of water is a physical change
But when egg is boiling the contents of the egg undergo permanent, irreversible chemical changes. So, boiling of egg is a chemical change.
XI.) Assertion – Reason type question
1.) Assertion: The explosion of fire cracker is a physical change.
Reason: A physical change is a reversible change.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true but R is false.
d.) A is false but R is true.
Answer : d. A is false but R is true.
2.) Assertion: The process of conversion of liquid water to its vapours by heating the liquid is called boiling.
Reason: The process of conversion of water vapours to liquid by cooling the vapours is called condensation.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true but R is false.
d.) A is false but R is true.
Answer : b. Both A and R are true but R is not the correct explanation of A.
3.) Assertion: Burning of wood log to charcoal is a physical change.
Reason: The products formed of burning a piece of wood can be easily converted back to wood log.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true but R is false.
d.) A is false but R is true.
Answer : both assertion and reason are false
4.) Assertion: The formation of iron oxide from iron is a chemical change.
Reason: For the rust to form from iron, it must be exposed to air and water.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true but R is false.
d.) A is false but R is true.
Answer : a. Both A and R are true and R is the correct explanation of A.
5.) Assertion: A drop of petrol when touched with finger gives a chill feeling.
Reason: The above phenomenon is an endothermic one.
a.) Both A and R are true and R is the correct explanation of A.
b.) Both A and R are true but R is not the correct explanation of A.
c.) A is true but R is false.
d.) A is false but R is true.
Answer : a. Both A and R are true and R is the correct explanation of A.
XII.) Picture based question
1.) Observe the picture and list down the changes that are accompanied in the picture.
a) ……………Solid wax becomes liquid………..
b) …………The liquid turns into gas and burns………….
c) ………………The molten liquid wax condenses into solid wax at the bottom……….
2.) Observe the picture containing a kettle and note that it has salt water in it and answer the following questions:
a) What is name of the process that is done to the kettle?
Answer : Boiling
b) What will happen to the content of the kettle?
Answer : Water in the kettle becomes steam.
c) What kind of change is occurring on the cold surface of the metal plate?
Answer : physical change
d) What can you say about the quality of water that is obtained in the beaker?
Answer : The water obtained in the beaker is pure. It is free from all kinds of salts.