Physical and Chemical Changes| Worksheet Solutions| Class 7

Worksheet solutions for chapter: Physical and Chemical Changes for class 7 are provided below.

(1) What is rusting? Give an example of it?

Ans-

Rusting is a process in which the iron products get a brownish substance on them in the presence of oxygen and water. This brownish substance, Iron oxide is called rust.

Chemical reaction is given below:

Iron (Fe) + Oxygen (O2) + Water (H2O) → rust(iron oxide Fe2O3)

If the moisture in air is high rusting becomes faster.

 

(2) Define chemical change with examples.

Ans-

A change in which one or more new substances are formed is called chemical change. It is also known as chemical reaction.

Eg:- Medicines, plastic, detergent etc are produced by chemical change.

In addition to new products other changes can occurs in a chemical change which are given below:

(i)Heat, light or any other radiation may be given off or absorbed.

Eg:-Burning of any substance

(ii) Sound may be produced.

Eg:- Explosion of fireworks that produces light, heat, sound and gases.

(iii)A change in smell may take place or a new smell may be given off.

Eg:-Rotten food items produce smell.

(iv) A colour change may take place.

Eg:- colour of apple, potato and brinjal slice changed to brown if it is not consumed immediately.

(v) A gas may be formed.

Eg:- Explosion of fireworks, candle flame produces gas.

 

(3) Identify physical change and chemical change involved in the following processes:

(i) Burning of wood

(ii) Cutting vegetables

(iii) Rust on nail

(iv) Making crystal of salt

Ans-

Physical and chemical change of the given processes are showing below:

S.N. Processes Physical/chemical change
(i) Burning of wood Chemical change
(ii) Cutting vegetables Physical change
(iii) Rust on nail Chemical change
(iv) Making crystal of salt Physical change

 

(4) Why dissolving of salt in water is a physical change?

Ans-

Dissolving of salt in water is a physical change because salt can be get back after evaporating water.

 

(5) Cooking omelets is a chemical change. Give reason.

Ans-

Cooking omelet is a chemical change because omelet is a new substance which we obtained in the process. It can not change in to raw egg.

 

(6) Fill in the blanks:

(i) ……is an example of physical change.

(ii)The process of depositing a layer of zinc on iron is called…..

(iii) The colour of copper sulphate solution is….

Ans-

(i)Crystalisation is an example of physical change.

(ii)The process of depositing a layer of zinc on iron is called rusting.

(iii) The colour of copper sulphate solution is blue.

 

(7) Write ‘T’ if statement is true and write ‘F’ if statement is false.

(i) Blowing balloon is a chemical change.

(ii) Photosynthesis is a chemical change.

(iii) Steel does not rust.

Ans-

(i) Blowing balloon is a chemical change.  F

(ii) Photosynthesis is a chemical change.  T

(iii) Steel does not rust.  T

 

(8) Why iron chair in garden acquire a brown colour substance after some time?

Ans-

Iron chair in garden acquire a brown colour substance after some time because iron acted with oxygen and water and produce new substance iron oxide. It is called rust and has brown colour.

Chemical reaction is given below:

Iron (Fe) + Oxygen (O2) + Water (H2O) → rust(iron oxide Fe2O3)

 

Choose the correct answer:

(9) Inflating of bicycle tube is a

(i) chemical change.

(ii) physical change.

Ans-

(ii) physical change.  

 

(10) Making chocolate shake is a

(i) physical change.

(ii) chemical change.

Ans-

(ii) chemical change. 

 

Helping Topics

Physical and Chemical Changes

NCERT Solutions Class 7