Selina Textbook Solutions: Physical and Chemical Changes | Chemistry Class 8 ICSE PDF Download

 Page 1


Physical and Chemical Changes 
Points to Remember: 
• All changes are classified into two types 
(i) Physical change (ii) Chemical change. 
• Physical Change— A physical change is a temporary change in which no new 
substance is formed and chemical composition remains same. e.g. Melting of ice. 
• Chemical Change— A chemical change is a permanent change, in which a new 
substances are formed whose chemical composition and physical properties are 
different, e.g. Burning of a candle. 
• Chemical Reaction— Any chemical change in matter involving its transformation 
into one or more new substances is called a chemical reaction. 
• Chemical Equations— A chemical equation is the symbolic representation of a 
chemical reaction using the symbols and the formulae of the substances involved 
in the reaction. 
• The substances that react with one another are called reactants, and the new 
substances thus formed are called products. 
• A balanced chemical reaction is one in which the number of the atoms of each 
element on the reactant side is equal to the number of atoms of that element on 
the product side. 
• The law of conservation of mass states that mass can neither be created nor be 
destroyed. 
• A chemical equation gives both qualitative and quantitative information about 
reactants and products. 
• The type of chemical reaction in which two substances combine to form a new 
substance is known as combination reaction. 
• The type of chemical reaction in which a substance breaks up on heating to form 
two or more simpler substances, which can be either elements or compounds, 
known as decomposition reaction. 
Activity 2 
Take a carrot and cut it into pieces. 
Now answer the following questions: 
Question 1. 
Is the change temporary? 
Answer: 
No. 
Question 2. 
Is the change reversible? 
Page 2


Physical and Chemical Changes 
Points to Remember: 
• All changes are classified into two types 
(i) Physical change (ii) Chemical change. 
• Physical Change— A physical change is a temporary change in which no new 
substance is formed and chemical composition remains same. e.g. Melting of ice. 
• Chemical Change— A chemical change is a permanent change, in which a new 
substances are formed whose chemical composition and physical properties are 
different, e.g. Burning of a candle. 
• Chemical Reaction— Any chemical change in matter involving its transformation 
into one or more new substances is called a chemical reaction. 
• Chemical Equations— A chemical equation is the symbolic representation of a 
chemical reaction using the symbols and the formulae of the substances involved 
in the reaction. 
• The substances that react with one another are called reactants, and the new 
substances thus formed are called products. 
• A balanced chemical reaction is one in which the number of the atoms of each 
element on the reactant side is equal to the number of atoms of that element on 
the product side. 
• The law of conservation of mass states that mass can neither be created nor be 
destroyed. 
• A chemical equation gives both qualitative and quantitative information about 
reactants and products. 
• The type of chemical reaction in which two substances combine to form a new 
substance is known as combination reaction. 
• The type of chemical reaction in which a substance breaks up on heating to form 
two or more simpler substances, which can be either elements or compounds, 
known as decomposition reaction. 
Activity 2 
Take a carrot and cut it into pieces. 
Now answer the following questions: 
Question 1. 
Is the change temporary? 
Answer: 
No. 
Question 2. 
Is the change reversible? 
Answer: 
No. 
Question 3. 
Why is cutting of carrot into pieces a physical change? 
Answer: 
Because there is no change in the property or chemical composition of the original 
substance i.e., carrot, and change is only in the state, size, shape, colour, texture or the 
smell of some or all of the substances that undergo physical change. 
Exercise 
Question 1. 
Define: 
(a) a physical change, (b) a chemical change. 
Answer: 
(a) Physical Change: A physical change is a temporary change in which no new 
substance is formed and the chemical composition of the original substance remains 
the same, even though its physical properties like colour, state, shape, size etc. might 
change. 
(b) Chemical Change: A chemical change is permanent change in which new 
substances are formed whose chemical composition and physical and chemical 
properties are different from those of in original substance. 
Question 2. 
Classify the following as a physical or a chemical change. 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(c) Butter getting rancid 
(d) Boiling of water 
(e) Burning of paper 
(f) Melting of wax 
(g) Burning of coal 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb 
(k) Curdling of milk 
Answer: 
Physical change 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(d) Boiling of water 
(f) Melting of wax 
(h) Formation of clouds 
(i) Making of a sugar solution 
Page 3


Physical and Chemical Changes 
Points to Remember: 
• All changes are classified into two types 
(i) Physical change (ii) Chemical change. 
• Physical Change— A physical change is a temporary change in which no new 
substance is formed and chemical composition remains same. e.g. Melting of ice. 
• Chemical Change— A chemical change is a permanent change, in which a new 
substances are formed whose chemical composition and physical properties are 
different, e.g. Burning of a candle. 
• Chemical Reaction— Any chemical change in matter involving its transformation 
into one or more new substances is called a chemical reaction. 
• Chemical Equations— A chemical equation is the symbolic representation of a 
chemical reaction using the symbols and the formulae of the substances involved 
in the reaction. 
• The substances that react with one another are called reactants, and the new 
substances thus formed are called products. 
• A balanced chemical reaction is one in which the number of the atoms of each 
element on the reactant side is equal to the number of atoms of that element on 
the product side. 
• The law of conservation of mass states that mass can neither be created nor be 
destroyed. 
• A chemical equation gives both qualitative and quantitative information about 
reactants and products. 
• The type of chemical reaction in which two substances combine to form a new 
substance is known as combination reaction. 
• The type of chemical reaction in which a substance breaks up on heating to form 
two or more simpler substances, which can be either elements or compounds, 
known as decomposition reaction. 
Activity 2 
Take a carrot and cut it into pieces. 
Now answer the following questions: 
Question 1. 
Is the change temporary? 
Answer: 
No. 
Question 2. 
Is the change reversible? 
Answer: 
No. 
Question 3. 
Why is cutting of carrot into pieces a physical change? 
Answer: 
Because there is no change in the property or chemical composition of the original 
substance i.e., carrot, and change is only in the state, size, shape, colour, texture or the 
smell of some or all of the substances that undergo physical change. 
Exercise 
Question 1. 
Define: 
(a) a physical change, (b) a chemical change. 
Answer: 
(a) Physical Change: A physical change is a temporary change in which no new 
substance is formed and the chemical composition of the original substance remains 
the same, even though its physical properties like colour, state, shape, size etc. might 
change. 
(b) Chemical Change: A chemical change is permanent change in which new 
substances are formed whose chemical composition and physical and chemical 
properties are different from those of in original substance. 
Question 2. 
Classify the following as a physical or a chemical change. 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(c) Butter getting rancid 
(d) Boiling of water 
(e) Burning of paper 
(f) Melting of wax 
(g) Burning of coal 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb 
(k) Curdling of milk 
Answer: 
Physical change 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(d) Boiling of water 
(f) Melting of wax 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb. 
Chemical change 
(c) Butter getting rancid 
(e) Burning of paper 
(g) Burning of coal 
(k) Curdling of milk 
Question 3. 
Fill in the blanks. 
Answer: 
(a) The process of a liquid changing into a solid is called freezing. 
(b) A change, which alters the composition of a substances, is known as 
a chemical change. 
(c) There is no change in the composition of the substance during a physical change. 
(d) The reaction in which energy is evolved is called exothermic reaction. 
Question 4. 
Given reason: 
(a) Freezing of water to ice and evaporation of water are physical changes. 
(b) Burning of a candle is both a physical and chemical change. 
(e) Burning of paper is a chemical change. 
(d) Cutting of a cloth piece is a physical change, though it cannot be reversed. 
Answer: 
(a) Freezing of water to ice and evaporation of water are physical change because 
water can be brought back to its original (liquid) form by 
1. We can heat the ice to bring it back to water. 
2. We can cool down the vapours to bring it back to water. 
(b) When a candle is lighted, some of the solid wax first melts and turns into liquid, then 
it turns into vapours to produce a flame. New substances CO2 and H2O vapours are 
formed alongwith the evolution of light and heat energy. This shows a chemical change. 
When some of the molten wax drops to the floor, it again solidifies. Which shows a 
physical change. Thus the melting of candle wax is a physical change and the 
production of CO2 and H2O represents chemical change. 
(c) When a piece of paper is burnt a new substance ash is produced. Even when the 
burning is stopped, the ash cannot be changed back into paper. This shows that the 
formation of the ash from paper is a permanent and irreversible change. 
(d) Because it does not change chemical composition of cloth and the change is only in 
the state, size, shape, colour, texture or the smell of some or all of the substances that 
undergo physical change. 
Page 4


Physical and Chemical Changes 
Points to Remember: 
• All changes are classified into two types 
(i) Physical change (ii) Chemical change. 
• Physical Change— A physical change is a temporary change in which no new 
substance is formed and chemical composition remains same. e.g. Melting of ice. 
• Chemical Change— A chemical change is a permanent change, in which a new 
substances are formed whose chemical composition and physical properties are 
different, e.g. Burning of a candle. 
• Chemical Reaction— Any chemical change in matter involving its transformation 
into one or more new substances is called a chemical reaction. 
• Chemical Equations— A chemical equation is the symbolic representation of a 
chemical reaction using the symbols and the formulae of the substances involved 
in the reaction. 
• The substances that react with one another are called reactants, and the new 
substances thus formed are called products. 
• A balanced chemical reaction is one in which the number of the atoms of each 
element on the reactant side is equal to the number of atoms of that element on 
the product side. 
• The law of conservation of mass states that mass can neither be created nor be 
destroyed. 
• A chemical equation gives both qualitative and quantitative information about 
reactants and products. 
• The type of chemical reaction in which two substances combine to form a new 
substance is known as combination reaction. 
• The type of chemical reaction in which a substance breaks up on heating to form 
two or more simpler substances, which can be either elements or compounds, 
known as decomposition reaction. 
Activity 2 
Take a carrot and cut it into pieces. 
Now answer the following questions: 
Question 1. 
Is the change temporary? 
Answer: 
No. 
Question 2. 
Is the change reversible? 
Answer: 
No. 
Question 3. 
Why is cutting of carrot into pieces a physical change? 
Answer: 
Because there is no change in the property or chemical composition of the original 
substance i.e., carrot, and change is only in the state, size, shape, colour, texture or the 
smell of some or all of the substances that undergo physical change. 
Exercise 
Question 1. 
Define: 
(a) a physical change, (b) a chemical change. 
Answer: 
(a) Physical Change: A physical change is a temporary change in which no new 
substance is formed and the chemical composition of the original substance remains 
the same, even though its physical properties like colour, state, shape, size etc. might 
change. 
(b) Chemical Change: A chemical change is permanent change in which new 
substances are formed whose chemical composition and physical and chemical 
properties are different from those of in original substance. 
Question 2. 
Classify the following as a physical or a chemical change. 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(c) Butter getting rancid 
(d) Boiling of water 
(e) Burning of paper 
(f) Melting of wax 
(g) Burning of coal 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb 
(k) Curdling of milk 
Answer: 
Physical change 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(d) Boiling of water 
(f) Melting of wax 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb. 
Chemical change 
(c) Butter getting rancid 
(e) Burning of paper 
(g) Burning of coal 
(k) Curdling of milk 
Question 3. 
Fill in the blanks. 
Answer: 
(a) The process of a liquid changing into a solid is called freezing. 
(b) A change, which alters the composition of a substances, is known as 
a chemical change. 
(c) There is no change in the composition of the substance during a physical change. 
(d) The reaction in which energy is evolved is called exothermic reaction. 
Question 4. 
Given reason: 
(a) Freezing of water to ice and evaporation of water are physical changes. 
(b) Burning of a candle is both a physical and chemical change. 
(e) Burning of paper is a chemical change. 
(d) Cutting of a cloth piece is a physical change, though it cannot be reversed. 
Answer: 
(a) Freezing of water to ice and evaporation of water are physical change because 
water can be brought back to its original (liquid) form by 
1. We can heat the ice to bring it back to water. 
2. We can cool down the vapours to bring it back to water. 
(b) When a candle is lighted, some of the solid wax first melts and turns into liquid, then 
it turns into vapours to produce a flame. New substances CO2 and H2O vapours are 
formed alongwith the evolution of light and heat energy. This shows a chemical change. 
When some of the molten wax drops to the floor, it again solidifies. Which shows a 
physical change. Thus the melting of candle wax is a physical change and the 
production of CO2 and H2O represents chemical change. 
(c) When a piece of paper is burnt a new substance ash is produced. Even when the 
burning is stopped, the ash cannot be changed back into paper. This shows that the 
formation of the ash from paper is a permanent and irreversible change. 
(d) Because it does not change chemical composition of cloth and the change is only in 
the state, size, shape, colour, texture or the smell of some or all of the substances that 
undergo physical change. 
Question 5. 
Give four difference between physical and chemical changes. 
Answer: 
The differences are Physical and Chemical Changes: 
Physical change 
1. In a physical change no new substance is formed and the chemical composition of 
substance remains same. There are changes only in physical properties and 
state. 
2. Temporaiy change which can be reversed by simple physical methods. 
3. Weight of original substance doesn’t change 
4. Energy like heat, light etc. may or may not be absorbed or released 
Chemical change 
1. In a chemical change new substance with entirely different chemical composition 
and properties is formed. 
2. Permanent change and irreversible 
3. Weight of original substances may increase or decrease 
4. Energy like heat, light etc. are given out or absorbed. 
ADDITIONAL QUESTIONS 
Check Your Progress 1 
1. Is melting of ice a reversible change ? 
True 
2. Change of seasons is a non-periodic change. True or false ? 
False. Change of seasons is a periodic change. 
3. In a physical change no net energy change is involved. True or false ? 
True 
4. New substances are formed in a chemical change. True or false ? 
True 
Check Your Progress 2 
1. Dissolving of a solid in liquid is a physical change. True or false ? 
True 
2. Is the process of digestion a physical change or chemical change ? 
Chemical 
3. During a physical change energy is either given out or absorbed by the system. 
True or false ? 
True 
Page 5


Physical and Chemical Changes 
Points to Remember: 
• All changes are classified into two types 
(i) Physical change (ii) Chemical change. 
• Physical Change— A physical change is a temporary change in which no new 
substance is formed and chemical composition remains same. e.g. Melting of ice. 
• Chemical Change— A chemical change is a permanent change, in which a new 
substances are formed whose chemical composition and physical properties are 
different, e.g. Burning of a candle. 
• Chemical Reaction— Any chemical change in matter involving its transformation 
into one or more new substances is called a chemical reaction. 
• Chemical Equations— A chemical equation is the symbolic representation of a 
chemical reaction using the symbols and the formulae of the substances involved 
in the reaction. 
• The substances that react with one another are called reactants, and the new 
substances thus formed are called products. 
• A balanced chemical reaction is one in which the number of the atoms of each 
element on the reactant side is equal to the number of atoms of that element on 
the product side. 
• The law of conservation of mass states that mass can neither be created nor be 
destroyed. 
• A chemical equation gives both qualitative and quantitative information about 
reactants and products. 
• The type of chemical reaction in which two substances combine to form a new 
substance is known as combination reaction. 
• The type of chemical reaction in which a substance breaks up on heating to form 
two or more simpler substances, which can be either elements or compounds, 
known as decomposition reaction. 
Activity 2 
Take a carrot and cut it into pieces. 
Now answer the following questions: 
Question 1. 
Is the change temporary? 
Answer: 
No. 
Question 2. 
Is the change reversible? 
Answer: 
No. 
Question 3. 
Why is cutting of carrot into pieces a physical change? 
Answer: 
Because there is no change in the property or chemical composition of the original 
substance i.e., carrot, and change is only in the state, size, shape, colour, texture or the 
smell of some or all of the substances that undergo physical change. 
Exercise 
Question 1. 
Define: 
(a) a physical change, (b) a chemical change. 
Answer: 
(a) Physical Change: A physical change is a temporary change in which no new 
substance is formed and the chemical composition of the original substance remains 
the same, even though its physical properties like colour, state, shape, size etc. might 
change. 
(b) Chemical Change: A chemical change is permanent change in which new 
substances are formed whose chemical composition and physical and chemical 
properties are different from those of in original substance. 
Question 2. 
Classify the following as a physical or a chemical change. 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(c) Butter getting rancid 
(d) Boiling of water 
(e) Burning of paper 
(f) Melting of wax 
(g) Burning of coal 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb 
(k) Curdling of milk 
Answer: 
Physical change 
(a) Drying of wet clothes 
(b) Manufacture of salt from sea water 
(d) Boiling of water 
(f) Melting of wax 
(h) Formation of clouds 
(i) Making of a sugar solution 
(j) Glowing of an electric bulb. 
Chemical change 
(c) Butter getting rancid 
(e) Burning of paper 
(g) Burning of coal 
(k) Curdling of milk 
Question 3. 
Fill in the blanks. 
Answer: 
(a) The process of a liquid changing into a solid is called freezing. 
(b) A change, which alters the composition of a substances, is known as 
a chemical change. 
(c) There is no change in the composition of the substance during a physical change. 
(d) The reaction in which energy is evolved is called exothermic reaction. 
Question 4. 
Given reason: 
(a) Freezing of water to ice and evaporation of water are physical changes. 
(b) Burning of a candle is both a physical and chemical change. 
(e) Burning of paper is a chemical change. 
(d) Cutting of a cloth piece is a physical change, though it cannot be reversed. 
Answer: 
(a) Freezing of water to ice and evaporation of water are physical change because 
water can be brought back to its original (liquid) form by 
1. We can heat the ice to bring it back to water. 
2. We can cool down the vapours to bring it back to water. 
(b) When a candle is lighted, some of the solid wax first melts and turns into liquid, then 
it turns into vapours to produce a flame. New substances CO2 and H2O vapours are 
formed alongwith the evolution of light and heat energy. This shows a chemical change. 
When some of the molten wax drops to the floor, it again solidifies. Which shows a 
physical change. Thus the melting of candle wax is a physical change and the 
production of CO2 and H2O represents chemical change. 
(c) When a piece of paper is burnt a new substance ash is produced. Even when the 
burning is stopped, the ash cannot be changed back into paper. This shows that the 
formation of the ash from paper is a permanent and irreversible change. 
(d) Because it does not change chemical composition of cloth and the change is only in 
the state, size, shape, colour, texture or the smell of some or all of the substances that 
undergo physical change. 
Question 5. 
Give four difference between physical and chemical changes. 
Answer: 
The differences are Physical and Chemical Changes: 
Physical change 
1. In a physical change no new substance is formed and the chemical composition of 
substance remains same. There are changes only in physical properties and 
state. 
2. Temporaiy change which can be reversed by simple physical methods. 
3. Weight of original substance doesn’t change 
4. Energy like heat, light etc. may or may not be absorbed or released 
Chemical change 
1. In a chemical change new substance with entirely different chemical composition 
and properties is formed. 
2. Permanent change and irreversible 
3. Weight of original substances may increase or decrease 
4. Energy like heat, light etc. are given out or absorbed. 
ADDITIONAL QUESTIONS 
Check Your Progress 1 
1. Is melting of ice a reversible change ? 
True 
2. Change of seasons is a non-periodic change. True or false ? 
False. Change of seasons is a periodic change. 
3. In a physical change no net energy change is involved. True or false ? 
True 
4. New substances are formed in a chemical change. True or false ? 
True 
Check Your Progress 2 
1. Dissolving of a solid in liquid is a physical change. True or false ? 
True 
2. Is the process of digestion a physical change or chemical change ? 
Chemical 
3. During a physical change energy is either given out or absorbed by the system. 
True or false ? 
True 
4. In a chemical change, rearrangement of molecules and atoms involves some 
energy changes. True or false ? 
True 
5. Energy in the form of 999 is absorbed during pho tosynthesis. 
Energy in the form of sunlight is absorbed during photosynthesis. 
EXERCISES 
A. Tick the most appropriate answer. 
1. Melting of ice is a 
1. reversible change 
2. irreversible change 
3. chemical change 
4. none of these 
2. Rising and setting of the sun at a given place is a 
1. periodic change 
2. undesirable change 
3. physical change 
4. reversible change 
3. Physical changes are 
1. permanent. 
2. periodic, 
3. temporary 
4. irreversible. 
4. Chemical changes involve 
1. change in shape. 
2. change in size. 
3. change in molecular composition. 
4. none of these 
5. Photosynthesis requires 
1. heat energy. 
2. wind energy 
3. sunlight. 
4. sound energy.