Question

Curdling of milk is physical or chemical changes.

Answer 1

Physical change: a temporary change, in which no new substance is formed and the chemical composition of the original substance remains the same, even though some of its physical properties like color, state, shape, size, etc. may change.

Characteristics of physical change:

• Identity of substance is maintained.
• The change is temporary
• There is a change in the physical state of the substance but chemical properties remain the same.

Chemical change: A permanent change in which new substances are formed whose chemical and physical properties are completely different from that those of the original substance.

Characteristics of chemical change:

• change is permanent and cannot be reversed.
• one or more new substance is formed.
• composition of the original substance does not remain the same.
• the heat or light may be produced or consumed during the reaction.
• exchange of energy takes place during the reaction.

During the curdling of milk, the composition of milk and curd is entirely different and the change is irreversible i.e. once the curd is formed it cannot be transformed back to milk. Thus it is a chemical change.