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We see a variety of changes taking place all around us everyday. Some changes involve one substance, whereas others involve more substances. Some changes that we come across daily are dissolving sugar in water, evaporation of water, sublimation of camphor, cutting of paper, conversion of milk into curd, etc. The changes are mainly of two types: physical changes and chemical changes. The changes that include change in the physical properties of a substance are physical changes, and the changes that include change in chemical properties of a substance are chemical changes. Physical properties include change in shape, size, colour and state of a substance.
Physical Change
A physical change can be defined as a change in which a substance undergoes change in its physical properties. It describes the change in physical nature of the substance.
Properties of a physical change
The physical changes are the temporary changes.
In a physical change no new substance is formed.
It is generally reversible, and we can recover the original substance in a physical change.
It may involve a temporary change in colour.
Very little amount of energy is absorbed or evolved in a physical change.
In a physical change, the composition remains the same, but the molecules rearrange themselves.
It only affects the physical properties of a substance.
Physical change and Chemical change
In a physical change, no new substance is formed, whereas the formation of a new substance marks the occurrence of a chemical change.
Physical change involves the change in physical properties of a substance, whereas chemical changes involve the change in physical as well as chemical properties of the substances.
In general, a physical change is a reversible process, whereas a chemical change is an irreversible process.
No energy is generated in a physical change, but in a chemical change, energy is generated, generally in the form of heat.
Physical change generally involves temporary changes, whereas in general, chemical changes lead to permanent changes.
Examples of physical changes
Heating and cooling
Certain elements and compounds present in nature can change their state of matter from solids to liquids and from liquids to gases when heated.
This process is reversible when the temperature is lowered.
This comprises a change in the physical properties of a substance which marks the physical change.
For example- melting of an ice cube into water, boiling of water by the process of evaporation, freezing of water to make ice cubes. All these examples represent an example of a physical change experiment.
Magnetism
Certain materials form permanent magnets by the mechanism of ferromagnetism. Ferro-magnetic materials can become magnetic, which comprises a physical change.
This process of ferromagnetism is reversible, and it does not affect the chemical composition of a substance.
It also involves the temporary change in the ferro-magnetic substances.
For example- a mixture of iron filings and sand is impossible to separate with a sieve. But it can be easily separated when we pass a magnet through a mixture containing iron. The magnet attracts the iron filings and pulls them from the sand. This represents an example of a physical change experiment.
Crystallisation
Some elements and compounds form crystals. When the metals form crystals their physical properties including strength and ductility changes.
The shape and size of a crystal can also be changed by physical hammering, rolling and by providing heat.
For example- carbon forms different kinds of crystals such as diamond, graphite, graphene, etc.
Mixtures
The mixture of substances which are not soluble are generally separated physically. For example- mixing of sand and pebbles, mixing of pulses and rice.
Some soluble mixtures are also reversible and represent physical phenomena. Most of the solutions of salt and sugar can be separated easily by evaporation; several other mixtures can be separated by different processes such as fractional distillation.
For example- mixing dirt and water to make mud, solution of salt and sugar, mixing alcohol and water, etc.
Alloys
Alloys comprise the mixture of different metal elements. Their separation is quite difficult, but in most of the cases, it can be done by physical means.
For example- brass is an alloy of copper and zinc.
Alloys where mercury is one of the metals can be separated physically by melting the alloy and boiling the mercury off as a vapour.
Some of the examples of physical changes that we see around us includes:
Melting of ice cubes into water
Freeze-drying fruits
Dissolving a drink mix into water
Chopping a vegetable into pieces
Evaporating puddles
Mixing of salt or sugar with water
Bending wire
Melting crayons
Conclusion
In general, changes can be classified into two types: physical changes and chemical changes. In a physical change, only the physical properties of a substance changes. Usually the physical properties describe the appearance of an object, whereas in a chemical change, both the physical as well as the chemical properties of a substance changes. In a physical change, the composition remains the same, but the molecules rearrange themselves. It only affects the physical properties of a substance. Some of the examples of physical changes that we see around us include: freezing of water to make ice cubes, freeze-drying fruits, dissolving a drink mix into water, chopping a vegetable into pieces, evaporating puddles, mixing dirt and water to make mud, bending wire and melting crayons.
