Today we are going to learn important concept of lesson Physical and chemical change .
⚫What are man made changes?
When the changes are done or produced by the man for his own wish the changes are called as man made changes. These changes can be either physical or chemical changes
Cutting vegetables and lightening an electric bulb are man made changes.
⚫What are natural changes?
Changes that are taken place naturally are known as natural changes .
fruit falling from a tree, rusting of iron
⚫What are useful and harmful changes?
Useful changes: the changes that are useful to us in day to day life are known as useful changes.
cooking food, baking bread ,sharpening the pencils
Harmful changes: the changes that are harmful to us or that are not useful for us are known as harmful changes.
spoiling of food and rusting of iron
⚫What are fast and slow changes?
Fast changes: the changes that are taking place rapidly or in a short interval of time are called as fast or quick changes
bursting of balloon
Slow changes: the changes that take place over a long period of time are called a slow changes.
rusting of iron
⚫What are reversible changes and irreversible changes?
Reversible changes: the changes that are happening in a forward and backward direction again and again are called as reversible changes.
melting of wax and obtaining the original wax again
Irreversible changes: the changes that can never occur backward direction it takes place only in forward directions are known as irreversible change.
milk into curd
Rusting of iron
⚫What are periodic and non periodic changes?
Periodic changes: the changes that are happening again and again after fixed interval of time are known as periodic changes.
sunrise and sunset
Non periodic changes: the changes that are not happening in again and again after fix interval of time are known as non periodic changes
⚫Water physical and chemical changes?
Physical changes are those changes in which substances changes from one form to another form without without the change in the basic characteristics. In this changes there is no formation of any type of new substances.
boiling ,melting freezing
Chemical changes are those changes in which new substances are formed.
ripening of fruits.
Rusting of iron.
Milk into curd
⚫What is corrosion?
Corrosion is caused due to the atmospheric attack of various oxygen moisture, vapour of chemicals in air .
rusting of iron takes place due to the atmospheric attack on the metal.
Similarly there is a formation of greenish layer on copper article. Due to the collision things becomes very weak.
⚫What is tining and galvanization?
Sometimes a thin coating of zinc is given on the iron articles so that it can be prevented from the corrosion this is called as galvanization.
Similarly a thin coating of tin is given on the copper and brass article so that it can be prevented from rusting is called as tining.
⚫Distinguish between physical change and chemical change
They are reversible change.
Composition of substances does not change.
They are irreversible change.
Composition of substances changes.
⚫Look at the picture and answer the following question.
➡️From the first picture it is clear that milk is converting into yoghurt and therefore this is a permanent chang
➡️From the second picture it is clear that ice is melting and there is a formation of water. therefore this is a physical change.
➡️From the third picture it is clear that seed is sprouting.
This is a natural change.
➡️From the fourth picture it is clear their water is boiling therefore it is a physical change.
➡️From the fifth picture firecrackers are exploding. This is a man made change which is chemical and irreversible in nature.
➡️In pictures 6th wood is on fire therefore this is a chemical change
➡️In picture number 7 again there is a fire crackers exploding therefore this is a man made change and chemical change and irreversible in nature.
⚫Tell the nature of change in the following case
➡️Raw mango is retaining…. It is permanent change
➡️The buds has bloomed into flowers
It is permanent changes
➡️Ice cubes in the glass have melted to form water
It is physical change aur temporary change
➡️Conversion of milk into curd
It is a chemical and irreversible change
➡️Stretching of a spring
It is reversible and physical change
➡️Revolution of earth around the sun
It is periodic, natural and slow change.
➡️Occurrence of an earthquake
It is natural, reversible, chemical as well as physical change.
➡️Bursting of crackers.
It is fast chemical and irreversible change.
⚫State the following sentences are true or false
➡️Rusting of iron is a chemical change.
This statement is true
➡️Evaporation is a physical change.
This statement is true.
➡️Melting of ice is a chemical change.
This statement is false.
➡️Cooking of food is physical change.
This statement is false.