Question 19
Give two examples for each of the following cases:
(a) Physical changes which are reversible.
(b) Physical changes which are not reversible.
(c) Chemical changes
Question 19
Give two examples for each of the following cases:
(a) Physical changes which are reversible.
(b) Physical changes which are not reversible.
(c) Chemical changes
(a) (i) Folding of paper is a physical change as in this process no new substance is formed and this process is reversible.
(ii) Melting of ice is a physical change as in this process ice will converts into liquid water, so there will be a change in the physical state not in the composition of water. There is no new chemical substances are formed and the transformation is reversible by freezing water which will turn the water back into ice.
(b) (i) Tearing of paper is a physical change as in this process no new substance is formed but after tearing paper we can not convert it into a whole paper. So, it is an irreversible process.
(ii) Breaking glass is a physical change as in this process no new substance is formed but after breaking glass, we can not convert it into as it was. So, it is an irreversible process.
(c) (i) Reaction between Magnesium and oxygen, in this process both magnesium and oxygen, react with each other and form a new product which is called magnesium oxide. Due to the formation of a new substance and this is an irreversible change, it is a chemical change.
(ii) Rusting of iron, In this process, when the iron is exposed to air and moisture, rust formation takes place i.e a new substance formed out of the reaction. The colour of the surface of the iron also changes. Hence, rusting of iron is a chemical change.This change is irreversible.
(a) (i) Folding of paper is a physical change as in this process no new substance is formed and this process is reversible.
(ii) Melting of ice is a physical change as in this process ice will converts into liquid water, so there will be a change in the physical state not in the composition of water. There is no new chemical substances are formed and the transformation is reversible by freezing water which will turn the water back into ice.
(b) (i) Tearing of paper is a physical change as in this process no new substance is formed but after tearing paper we can not convert it into a whole paper. So, it is an irreversible process.
(ii) Breaking glass is a physical change as in this process no new substance is formed but after breaking glass, we can not convert it into as it was. So, it is an irreversible process.
(c) (i) Reaction between Magnesium and oxygen, in this process both magnesium and oxygen, react with each other and form a new product which is called magnesium oxide. Due to the formation of a new substance and this is an irreversible change, it is a chemical change.
(ii) Rusting of iron, In this process, when the iron is exposed to air and moisture, rust formation takes place i.e a new substance formed out of the reaction. The colour of the surface of the iron also changes. Hence, rusting of iron is a chemical change.This change is irreversible.
